Serializer.cs source code in C# .NET

Source code for the .NET framework in C#

                        

Code:

/ 4.0 / 4.0 / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / DataWeb / Server / System / Data / Services / Serializers / Serializer.cs / 1305376 / Serializer.cs

                            //---------------------------------------------------------------------- 
// 
//      Copyright (c) Microsoft Corporation.  All rights reserved.
// 
//  
//      An abstract base serializer for various serializers
//  
// 
// @owner  [....]
//--------------------------------------------------------------------- 

namespace System.Data.Services.Serializers
{
    #region Namespaces. 

    using System; 
    using System.Collections; 
    using System.Collections.Generic;
    using System.Data.Services; 
    using System.Data.Services.Providers;
    using System.Diagnostics;
    using System.Text;
    using System.Data.Services.Internal; 

    #endregion Namespaces. 
 
    /// Abstract base class for all serializers.
    internal abstract class Serializer : IExceptionWriter 
    {
        #region Private fields.

        /// Maximum recursion limit on serializers. 
        private const int RecursionLimit = 100;
 
        ///  
        /// These query parameters can be copied for each next page link.
        /// Don't need to copy $skiptoken, $skip and $top because they are calculated every time. 
        /// 
        private static readonly String[] NextPageQueryParametersToCopy =
        {
            XmlConstants.HttpQueryStringFilter, 
            XmlConstants.HttpQueryStringExpand,
            XmlConstants.HttpQueryStringOrderBy, 
            XmlConstants.HttpQueryStringInlineCount, 
            XmlConstants.HttpQueryStringSelect
        }; 

        /// Base URI from which resources should be resolved.
        private readonly Uri absoluteServiceUri;
 
        /// Data provider from which metadata should be gathered.
        private readonly string httpETagHeaderValue; 
 
        /// Data provider from which metadata should be gathered.
        private readonly IDataService service; 

        /// Description for the requested results.
        private readonly RequestDescription requestDescription;
 
        /// Collection of complex types, used for cycle detection.
        private HashSet complexTypeCollection; 
 
        /// Resolved segment containers.
        private List segmentContainers; 

        /// Segment names.
        private List segmentNames;
 
        /// Result counts for segments.
        private List segmentResultCounts; 
 
        /// Depth of recursion.
        private int recursionDepth; 

        /// Current skip token object for custom paging.
        private object[] currentSkipTokenForCustomPaging;
 
        #endregion Private fields.
 
        /// Initializes a new base Serializer, ready to write out a description. 
        /// Description for the requested results.
        /// Base URI from which resources should be resolved. 
        /// Service with configuration and provider from which metadata should be gathered.
        /// HTTP ETag header value.
        internal Serializer(RequestDescription requestDescription, Uri absoluteServiceUri, IDataService service, string httpETagHeaderValue)
        { 
            Debug.Assert(requestDescription != null, "requestDescription != null");
            Debug.Assert(absoluteServiceUri != null, "absoluteServiceUri != null"); 
            Debug.Assert(service != null, "service != null"); 

            this.requestDescription = requestDescription; 
            this.absoluteServiceUri = absoluteServiceUri;
            this.service = service;
            this.httpETagHeaderValue = httpETagHeaderValue;
        } 

        /// Container for the resource being serialized (possibly null). 
        protected ResourceSetWrapper CurrentContainer 
        {
            get 
            {
                if (this.segmentContainers == null || this.segmentContainers.Count == 0)
                {
                    return this.requestDescription.LastSegmentInfo.TargetContainer; 
                }
                else 
                { 
                    return this.segmentContainers[this.segmentContainers.Count - 1];
                } 
            }
        }

        /// Is current container the root container. 
        protected bool IsRootContainer
        { 
            get 
            {
                return (this.segmentContainers == null || this.segmentContainers.Count == 1); 
            }
        }

        ///  
        /// Gets the Data provider from which metadata should be gathered.
        ///  
        protected DataServiceProviderWrapper Provider 
        {
            [DebuggerStepThrough] 
            get { return this.service.Provider; }
        }

        ///  
        /// Gets the Data service from which metadata should be gathered.
        ///  
        protected IDataService Service 
        {
            [DebuggerStepThrough] 
            get { return this.service; }
        }

        /// Gets the absolute URI to the service. 
        protected Uri AbsoluteServiceUri
        { 
            [DebuggerStepThrough] 
            get { return this.absoluteServiceUri; }
        } 

        /// 
        /// Gets the RequestDescription for the request that is getting serialized.
        ///  
        protected RequestDescription RequestDescription
        { 
            [DebuggerStepThrough] 
            get
            { 
                return this.requestDescription;
            }
        }
 
        /// Are we using custom paging?
        protected bool IsCustomPaged 
        { 
            get
            { 
                return this.service.PagingProvider.IsCustomPagedForSerialization;
            }
        }
 
        /// Serializes exception information.
        /// Description of exception to serialize. 
        public abstract void WriteException(HandleExceptionArgs args); 

        ///  
        /// Gets the uri given the list of resource properties. This logic must be the same across all
        /// serializers. Hence putting this in a util class
        /// 
        /// instance of the resource type whose properties needs to be returned 
        /// Provider from which resource was obtained.
        /// Container for the resource. 
        /// Base URI from which resources should be resolved. 
        /// uri for the given resource
        internal static Uri GetUri(object resource, DataServiceProviderWrapper provider, ResourceSetWrapper container, Uri absoluteServiceUri) 
        {
            Debug.Assert(container != null, "container != null");
            string objectKey = GetObjectKey(resource, provider, container.Name);
            return RequestUriProcessor.AppendEscapedSegment(absoluteServiceUri, objectKey); 
        }
 
        ///  
        /// Appends the given entry to the given uri
        ///  
        /// uri to which the entry needs to be appended
        /// entry which gets appended to the given uri
        /// new uri with the entry appended to the given uri
        internal static Uri AppendEntryToUri(Uri currentUri, string entry) 
        {
            return RequestUriProcessor.AppendUnescapedSegment(currentUri, entry); 
        } 

        ///  
        /// Handles the complete serialization for the specified .
        /// 
        /// Query results to enumerate.
        /// Whether  was succesfully advanced to the first element. 
        /// 
        ///  should correspond to the RequestQuery of the 
        /// RequestDescription object passed while constructing this serializer 
        /// We allow the results to be passed in
        /// to let the query be executed earlier than at result-writing time, which 
        /// helps detect data and query errors where they can be better handled.
        /// 
        internal void WriteRequest(IEnumerator queryResults, bool hasMoved)
        { 
            Debug.Assert(this.requestDescription.RequestEnumerable != null, "this.requestDescription.RequestEnumerable != null");
            Debug.Assert(queryResults != null, "queryResults != null"); 
            IExpandedResult expanded = queryResults as IExpandedResult; 

            if (this.requestDescription.LinkUri) 
            {
                bool needPop = this.PushSegmentForRoot();
                if (this.requestDescription.IsSingleResult)
                { 
                    this.WriteLink(queryResults.Current);
                    if (queryResults.MoveNext()) 
                    { 
                        throw new InvalidOperationException(Strings.SingleResourceExpected);
                    } 
                }
                else
                {
                    this.WriteLinkCollection(queryResults, hasMoved); 
                }
 
                this.PopSegmentName(needPop); 
            }
            else if (this.requestDescription.IsSingleResult) 
            {
                Debug.Assert(hasMoved == true, "hasMoved == true");
                this.WriteTopLevelElement(expanded, queryResults.Current);
                if (queryResults.MoveNext()) 
                {
                    throw new InvalidOperationException(Strings.SingleResourceExpected); 
                } 
            }
            else 
            {
                this.WriteTopLevelElements(expanded, queryResults, hasMoved);
            }
 
            this.Flush();
        } 
 
        /// Gets the expandable value for the specified object.
        /// underlying data source instance. 
        /// Expanded properties for the result, possibly null.
        /// Object with value to retrieve.
        /// Property for which value will be retrieved.
        /// The property value. 
        protected static object GetExpandedProperty(DataServiceProviderWrapper provider, IExpandedResult expanded, object customObject, ResourceProperty property)
        { 
            Debug.Assert(property != null, "property != null"); 
            if (expanded == null)
            { 
                return WebUtil.GetPropertyValue(provider, customObject, null, property, null);
            }
            else
            { 
                // We may end up projecting null as a value of ResourceSetReference property. This can in theory break
                //   the serializers as they expect a non-null (possibly empty) IEnumerable instead. But note that 
                //   if we project null into the expanded property, we also project null into the ExpandedElement property 
                //   and thus the serializers should recognize this value as null and don't try to expand its properties.
                Debug.Assert( 
                    expanded.ExpandedElement != null,
                    "We should not be accessing expanded properties on null resource.");
                return expanded.GetExpandedPropertyValue(property.Name);
            } 
        }
 
        /// Gets the expanded element for the specified expanded result. 
        /// The expanded result to process.
        /// The expanded element. 
        protected static object GetExpandedElement(IExpandedResult expanded)
        {
            Debug.Assert(expanded != null, "expanded != null");
            return expanded.ExpandedElement; 
        }
 
        /// Flushes the writer to the underlying stream. 
        protected abstract void Flush();
 
        /// Writes a single top-level element.
        /// Expanded properties for the result.
        /// Element to write, possibly null.
        protected abstract void WriteTopLevelElement(IExpandedResult expanded, object element); 

        /// Writes multiple top-level elements, possibly none. 
        /// Expanded properties for the result. 
        /// Result elements.
        /// Whether  was succesfully advanced to the first element. 
        protected abstract void WriteTopLevelElements(IExpandedResult expanded, IEnumerator elements, bool hasMoved);

        /// 
        /// Write out the entry count 
        /// 
        protected abstract void WriteRowCount(); 
 
        /// 
        /// Write out the uri for the given element 
        /// 
        /// element whose uri needs to be written out.
        protected abstract void WriteLink(object element);
 
        /// 
        /// Write out the uri for the given elements 
        ///  
        /// elements whose uri need to be writtne out
        /// the current state of the enumerator. 
        protected abstract void WriteLinkCollection(IEnumerator elements, bool hasMoved);

        /// 
        /// Adds the given object instance to complex type collection 
        /// 
        /// instance to be added 
        /// true, if it got added successfully 
        protected bool AddToComplexTypeCollection(object complexTypeInstance)
        { 
            if (this.complexTypeCollection == null)
            {
                this.complexTypeCollection = new HashSet(ReferenceEqualityComparer.Instance);
            } 

            return this.complexTypeCollection.Add(complexTypeInstance); 
        } 

        ///  
        /// Gets the skip token object contained in the expanded result for standard paging.
        /// 
        /// Current expanded result.
        /// Skip token object if any. 
        protected IExpandedResult GetSkipToken(IExpandedResult expanded)
        { 
            if (expanded != null && !this.IsCustomPaged && !this.RequestDescription.IsRequestForEnumServiceOperation) 
            {
                return expanded.GetExpandedPropertyValue(XmlConstants.HttpQueryStringSkipToken) as IExpandedResult; 
            }

            return null;
        } 

        ///  
        /// Obtains the URI for the link for next page in string format 
        /// 
        /// Last object serialized to be used for generating $skiptoken 
        /// The  of the $skiptoken property of object corresponding to last serialized object
        /// Absolute response URI
        /// URI for the link for next page
        protected String GetNextLinkUri(object lastObject, IExpandedResult skipTokenExpandedResult, Uri absoluteUri) 
        {
            UriBuilder builder = new UriBuilder(absoluteUri); 
            SkipTokenBuilder skipTokenBuilder = null; 

            if (this.IsRootContainer) 
            {
                if (!this.IsCustomPaged)
                {
                    if (skipTokenExpandedResult != null) 
                    {
                        skipTokenBuilder = new SkipTokenBuilderFromExpandedResult(skipTokenExpandedResult, this.RequestDescription.SkipTokenExpressionCount); 
                    } 
                    else
                    { 
                        Debug.Assert(this.RequestDescription.SkipTokenProperties != null, "Must have skip token properties collection");
                        Debug.Assert(this.RequestDescription.SkipTokenProperties.Count > 0, "Must have some valid ordered properties in the skip token properties collection");
                        skipTokenBuilder = new SkipTokenBuilderFromProperties(lastObject, this.Provider, this.RequestDescription.SkipTokenProperties);
                    } 
                }
                else 
                { 
                    Debug.Assert(this.currentSkipTokenForCustomPaging != null, "Must have obtained the skip token for custom paging.");
                    skipTokenBuilder = new SkipTokenBuilderFromCustomPaging(this.currentSkipTokenForCustomPaging); 
                }

                builder.Query = this.GetNextPageQueryParametersForRootContainer().Append(skipTokenBuilder.GetSkipToken()).ToString();
            } 
            else
            { 
                if (!this.IsCustomPaged) 
                {
                    // Internal results 
                    skipTokenBuilder = new SkipTokenBuilderFromProperties(lastObject, this.Provider, this.CurrentContainer.ResourceType.KeyProperties);
                }
                else
                { 
                    Debug.Assert(this.currentSkipTokenForCustomPaging != null, "Must have obtained the skip token for custom paging.");
                    skipTokenBuilder = new SkipTokenBuilderFromCustomPaging(this.currentSkipTokenForCustomPaging); 
                } 

                builder.Query = this.GetNextPageQueryParametersForExpandedContainer().Append(skipTokenBuilder.GetSkipToken()).ToString(); 
            }

            return builder.Uri.AbsoluteUri;
        } 

        /// Is next page link needs to be appended to the feed 
        /// Current result enumerator. 
        /// true if the feed must have a next page link
        protected bool NeedNextPageLink(IEnumerator enumerator) 
        {
            // For open types, current container could be null
            if (this.CurrentContainer != null && !this.RequestDescription.IsRequestForEnumServiceOperation)
            { 
                if (this.IsCustomPaged)
                { 
                    this.currentSkipTokenForCustomPaging = 
                        this.service.PagingProvider.PagingProviderInterface.GetContinuationToken(BasicExpandProvider.ExpandedEnumerator.UnwrapEnumerator(enumerator));
                    Debug.Assert( 
                            this.RequestDescription.ResponseVersion != RequestDescription.DataServiceDefaultResponseVersion,
                            "If custom paging is enabled, our response should be 2.0 and beyond.");

                    return this.currentSkipTokenForCustomPaging != null && this.currentSkipTokenForCustomPaging.Length > 0; 
                }
                else 
                { 
                    int pageSize = this.CurrentContainer.PageSize;
 
                    if (pageSize != 0 && this.RequestDescription.ResponseVersion != RequestDescription.DataServiceDefaultResponseVersion)
                    {
                        // For the root segment, if the $top parameter value is less than or equal to page size then we
                        // don't need to send the next page link. 
                        if (this.segmentResultCounts.Count == 1)
                        { 
                            int? topQueryParameter = this.GetTopQueryParameter(); 

                            if (topQueryParameter.HasValue) 
                            {
                                Debug.Assert(topQueryParameter.Value >= this.segmentResultCounts[this.segmentResultCounts.Count - 1], "$top must be the upper limits of the number of results returned.");
                                if (topQueryParameter.Value <= pageSize)
                                { 
                                    return false;
                                } 
                            } 
                        }
 
                        return this.segmentResultCounts[this.segmentResultCounts.Count - 1] == pageSize;
                    }
                }
            } 

            return false; 
        } 

        /// Pushes a segment for the root of the tree being written out. 
        /// Name of open property.
        /// Resulved type of open property.
        /// Calls to this method should be balanced with calls to PopSegmentName.
        /// true if segment was pushed, false otherwise 
        protected bool PushSegmentForOpenProperty(string propertyName, ResourceType propertyResourceType)
        { 
            Debug.Assert(propertyName != null, "propertyName != null"); 
            Debug.Assert(propertyResourceType != null, "propertyResourceType != null");
            ResourceSetWrapper container = null; 
            if (propertyResourceType.ResourceTypeKind == ResourceTypeKind.EntityType)
            {
                // Open navigation properties are not supported on OpenTypes.
                throw DataServiceException.CreateBadRequestError(Strings.OpenNavigationPropertiesNotSupportedOnOpenTypes(propertyName)); 
            }
 
            return this.PushSegment(propertyName, container); 
        }
 
        /// Increments the result count for the current segment, throws if exceeds the limit.
        protected void IncrementSegmentResultCount()
        {
            if (this.segmentResultCounts != null) 
            {
                Debug.Assert(this.segmentResultCounts.Count > 0, "this.segmentResultCounts.Count > 0 -- otherwise we didn't PushSegmentForRoot"); 
                int max = this.service.Configuration.MaxResultsPerCollection; 

                if (!this.IsCustomPaged) 
                {
                    // For Open types, current container could be null, even though MaxResultsPerCollection has been set
                    // set we need to check for container before we try to assume page size, also open types do not have
                    // page sizes so we can safely ignore this check here 
                    if (this.CurrentContainer != null && this.CurrentContainer.PageSize != 0)
                    { 
                        Debug.Assert(max == Int32.MaxValue, "Either page size or max result count can be set, but not both"); 
                        max = this.CurrentContainer.PageSize;
                    } 
                }

                if (max != Int32.MaxValue)
                { 
                    int count = this.segmentResultCounts[this.segmentResultCounts.Count - 1];
                    checked 
                    { 
                        count++;
                    } 

                    if (count > max)
                    {
                        throw DataServiceException.CreateBadRequestError(Strings.Serializer_ResultsExceedMax(max)); 
                    }
 
                    this.segmentResultCounts[this.segmentResultCounts.Count - 1] = count; 
                }
            } 
        }

        /// Pushes a segment from the stack of names being written.
        /// Property to push. 
        /// Calls to this method should be balanced with calls to PopSegmentName.
        /// true if a segment was pushed, false otherwise 
        protected bool PushSegmentForProperty(ResourceProperty property) 
        {
            Debug.Assert(property != null, "property != null"); 
            ResourceSetWrapper current = null;
            if ((property.Kind & (ResourcePropertyKind.ResourceReference | ResourcePropertyKind.ResourceSetReference)) != 0)
            {
                current = this.CurrentContainer; 
                if (current != null)
                { 
                    current = this.service.Provider.GetContainer(current, current.ResourceType, property); 
                }
            } 

            return this.PushSegment(property.Name, current);
        }
 
        /// Pushes a segment for the root of the tree being written out.
        /// Calls to this method should be balanced with calls to PopSegmentName. 
        /// true if the segment was pushed, false otherwise 
        protected bool PushSegmentForRoot()
        { 
            return this.PushSegment(this.RequestDescription.ContainerName, this.CurrentContainer);
        }

        /// Pops a segment name from the stack of names being written. 
        /// Is a pop required. Only true if last push was successful
        /// Calls to this method should be balanced with previous calls to PushSegmentName. 
        protected void PopSegmentName(bool needPop) 
        {
            if (this.segmentNames != null && needPop) 
            {
                Debug.Assert(this.segmentNames.Count > 0, "this.segmentNames.Count > 0");
                this.segmentNames.RemoveAt(this.segmentNames.Count - 1);
                this.segmentContainers.RemoveAt(this.segmentContainers.Count - 1); 
                this.segmentResultCounts.RemoveAt(this.segmentResultCounts.Count - 1);
                Debug.Assert( 
                    this.segmentContainers.Count == this.segmentNames.Count, 
                    "this.segmentContainers.Count == this.segmentNames.Count -- should always be one-to-one");
                Debug.Assert( 
                    this.segmentContainers.Count == this.segmentResultCounts.Count,
                    "this.segmentContainers.Count == this.segmentResultCounts.Count -- should always be one-to-one");
            }
        } 

        /// Marks the fact that a recursive method was entered, and checks that the depth is allowed. 
        protected void RecurseEnter() 
        {
            WebUtil.RecurseEnter(RecursionLimit, ref this.recursionDepth); 
        }

        /// Marks the fact that a recursive method is leaving.
        protected void RecurseLeave() 
        {
            WebUtil.RecurseLeave(ref this.recursionDepth); 
        } 

        /// Returns a clone of the segment names and containers trackd at this moment. 
        /// A clone of the segment names and containers tracked at this moment; possibly null.
        protected object SaveSegmentNames()
        {
            if (this.segmentNames == null) 
            {
                return null; 
            } 
            else
            { 
                return new object[3]
                {
                    new List(this.segmentNames),
                    new List(this.segmentContainers), 
                    new List(this.segmentResultCounts)
                }; 
            } 
        }
 
        /// Restores the segment names saved through .
        /// Value returned from a previous call to .
        protected void RestoreSegmentNames(object savedSegmentNames)
        { 
            object[] savedLists = (object[])savedSegmentNames;
            if (savedLists == null) 
            { 
                this.segmentNames = null;
                this.segmentContainers = null; 
                this.segmentResultCounts = null;
            }
            else
            { 
                this.segmentNames = (List)savedLists[0];
                this.segmentContainers = (List)savedLists[1]; 
                this.segmentResultCounts = (List)savedLists[2]; 
            }
        } 

        /// 
        /// Remove the given object instance from the complex type collection
        ///  
        /// instance to be removed
        protected void RemoveFromComplexTypeCollection(object complexTypeInstance) 
        { 
            Debug.Assert(this.complexTypeCollection != null, "this.complexTypeCollection != null");
            Debug.Assert(this.complexTypeCollection.Contains(complexTypeInstance), "this.complexTypeCollection.Contains(complexTypeInstance)"); 

            this.complexTypeCollection.Remove(complexTypeInstance);
        }
 
        /// Checks whether the property with the specified name should be expanded in-line.
        /// Name of property to consider for expansion. 
        /// true if the segment should be expanded; false otherwise. 
        protected bool ShouldExpandSegment(string name)
        { 
            Debug.Assert(name != null, "name != null");

            if (this.segmentNames == null)
            { 
                return false;
            } 
 
            if (this.requestDescription.RootProjectionNode != null)
            { 
                if (this.requestDescription.RootProjectionNode.UseExpandPathsForSerialization &&
                    this.requestDescription.RootProjectionNode.ExpandPaths != null)
                {
                    // We need to use the old ExpandPaths to determine which segments to expand 
                    //   since the IExpandProvider might have modified this collection.
                    for (int i = 0; i < this.requestDescription.RootProjectionNode.ExpandPaths.Count; i++) 
                    { 
                        List expandPath = this.requestDescription.RootProjectionNode.ExpandPaths[i];
                        if (expandPath.Count < this.segmentNames.Count) 
                        {
                            continue;
                        }
 
                        // We start off at '1' for segment names because the first one is the
                        // "this" in the query (/Customers?$expand=Orders doesn't include "Customers"). 
                        bool matchFound = true; 
                        for (int j = 1; j < this.segmentNames.Count; j++)
                        { 
                            if (expandPath[j - 1].Name != this.segmentNames[j])
                            {
                                matchFound = false;
                                break; 
                            }
                        } 
 
                        if (matchFound && expandPath[this.segmentNames.Count - 1].Name == name)
                        { 
                            return true;
                        }
                    }
                } 
                else
                { 
                    // We can use the new tree of expanded nodes to determine the expansions. 
                    // So find the expanded node on which we are now.
                    ExpandedProjectionNode expandedNode = this.GetCurrentExpandedProjectionNode(); 
                    if (expandedNode != null)
                    {
                        // And then if that node contains a child node of the specified name
                        //   and that child is also an expanded node, we should expand it. 
                        ProjectionNode lastNode = expandedNode.FindNode(name);
                        if (lastNode != null && lastNode is ExpandedProjectionNode) 
                        { 
                            return true;
                        } 
                    }
                }
            }
 
            return false;
        } 
 
        /// Returns a list of projection segments defined for the current segment.
        /// List of  describing projections for the current segment. 
        /// If this method returns null it means no projections are to be applied and the entire resource
        /// for the current segment should be serialized. If it returns non-null only the properties described
        /// by the returned projection segments should be serialized.
        protected IEnumerable GetProjections() 
        {
            ExpandedProjectionNode expandedProjectionNode = this.GetCurrentExpandedProjectionNode(); 
            if (expandedProjectionNode == null || expandedProjectionNode.ProjectAllProperties) 
            {
                return null; 
            }
            else
            {
                return expandedProjectionNode.Nodes; 
            }
        } 
 
        /// 
        /// Returns the ETag value from the host response header 
        /// 
        /// resource whose etag value gets to be returned
        /// returns the etag value for the given resource
        protected string GetETagValue(object resource) 
        {
            // this.httpETagHeaderValue is the etag value which got computed for writing the etag in the response 
            // headers. The etag response header only gets written out in certain scenarios, whereas we always 
            // write etag in the response payload, if the type has etag properties. So just checking here is the
            // etag has already been computed, and if yes, returning that, otherwise computing the etag. 
            if (!String.IsNullOrEmpty(this.httpETagHeaderValue))
            {
                return this.httpETagHeaderValue;
            } 
            else
            { 
                Debug.Assert(this.CurrentContainer != null, "this.CurrentContainer != null"); 
                return WebUtil.GetETagValue(this.service, resource, this.CurrentContainer);
            } 
        }

        /// Returns the key for the given resource.
        /// Resource for which key value needs to be returned. 
        /// Specific provider from which resource was obtained.
        /// name of the entity container that the resource belongs to 
        /// Key for the given resource, with values encoded for use in a URI. 
        private static string GetObjectKey(object resource, DataServiceProviderWrapper provider, string containerName)
        { 
            Debug.Assert(resource != null, "resource != null");
            Debug.Assert(provider != null, "provider != null");
            Debug.Assert(!String.IsNullOrEmpty(containerName), "container name must be specified");
 
            StringBuilder resultBuilder = new StringBuilder();
            resultBuilder.Append(containerName); 
            resultBuilder.Append('('); 
            ResourceType resourceType = WebUtil.GetNonPrimitiveResourceType(provider, resource);
            Debug.Assert(resourceType != null, "resourceType != null"); 
            IList keyProperties = resourceType.KeyProperties;
            Debug.Assert(keyProperties.Count != 0, "every resource type must have a key");
            for (int i = 0; i < keyProperties.Count; i++)
            { 
                ResourceProperty property = keyProperties[i];
                Debug.Assert(property.IsOfKind(ResourcePropertyKind.Key), "must be key property"); 
 
                object keyValue = WebUtil.GetPropertyValue(provider, resource, resourceType, property, null);
                if (keyValue == null) 
                {
                    // null keys not supported.
                    throw new InvalidOperationException(Strings.Serializer_NullKeysAreNotSupported(property.Name));
                } 

                if (i == 0) 
                { 
                    if (keyProperties.Count != 1)
                    { 
                        resultBuilder.Append(property.Name);
                        resultBuilder.Append('=');
                    }
                } 
                else
                { 
                    resultBuilder.Append(','); 
                    resultBuilder.Append(property.Name);
                    resultBuilder.Append('='); 
                }

                string keyValueText;
                if (!System.Data.Services.Parsing.WebConvert.TryKeyPrimitiveToString(keyValue, out keyValueText)) 
                {
                    throw new InvalidOperationException(Strings.Serializer_CannotConvertValue(keyValue)); 
                } 

                Debug.Assert(keyValueText != null, "keyValueText != null - otherwise TryKeyPrimitiveToString returned true and null value"); 
                resultBuilder.Append(System.Uri.EscapeDataString(keyValueText));
            }

            resultBuilder.Append(')'); 
            return resultBuilder.ToString();
        } 
 
        /// Helper method to append a path to the $expand or $select path list.
        /// The  to which to append the path. 
        /// The segments of the path up to the last segment.
        /// The last segment of the path.
        private static void AppendProjectionOrExpansionPath(StringBuilder pathsBuilder, List parentPathSegments, string lastPathSegment)
        { 
            if (pathsBuilder.Length != 0)
            { 
                pathsBuilder.Append(','); 
            }
 
            foreach (string parentPathSegment in parentPathSegments)
            {
                pathsBuilder.Append(parentPathSegment).Append('/');
            } 

            pathsBuilder.Append(lastPathSegment); 
        } 

        /// Finds the  node which describes the current segment. 
        /// The  which describes the current segment, or null
        /// if no such node is available.
        private ExpandedProjectionNode GetCurrentExpandedProjectionNode()
        { 
            ExpandedProjectionNode expandedProjectionNode = this.RequestDescription.RootProjectionNode;
            if (expandedProjectionNode == null) 
            { 
                return null;
            } 

            if (this.segmentNames != null)
            {
                // We start off at '1' for segment names because the first one is the 
                // "this" in the query and projection segments don't have that (the root is the "this")
                for (int i = 1; i < this.segmentNames.Count; i++) 
                { 
                    ProjectionNode projectionNode = expandedProjectionNode.FindNode(this.segmentNames[i]);
                    if (projectionNode == null) 
                    {
                        // If we don't have a projection node, report everything (complex types for example).
                        return null;
                    } 

                    Debug.Assert( 
                        projectionNode is ExpandedProjectionNode, 
                        "We have a pushed segment on the serialization stack which is not backed by expanded node in the query definition.");
                    expandedProjectionNode = (ExpandedProjectionNode)projectionNode; 
                }
            }

            return expandedProjectionNode; 
        }
 
        ///  
        /// Builds the string corresponding to query parameters for top level results to be put in next page link.
        ///  
        /// StringBuilder which has the query parameters in the URI query parameter format.
        private StringBuilder GetNextPageQueryParametersForRootContainer()
        {
            StringBuilder queryParametersBuilder = new StringBuilder(); 

            // Handle service operation parameters 
            if (this.RequestDescription.SegmentInfos[0].TargetSource == RequestTargetSource.ServiceOperation) 
            {
                foreach (var parameter in this.RequestDescription.SegmentInfos[0].Operation.Parameters) 
                {
                    if (queryParametersBuilder.Length > 0)
                    {
                        queryParametersBuilder.Append('&'); 
                    }
 
                    queryParametersBuilder.Append(parameter.Name).Append('='); 
                    queryParametersBuilder.Append(this.service.OperationContext.Host.GetQueryStringItem(parameter.Name));
                } 
            }

            foreach (String queryParameter in Serializer.NextPageQueryParametersToCopy)
            { 
                String value = this.service.OperationContext.Host.GetQueryStringItem(queryParameter);
                if (!String.IsNullOrEmpty(value)) 
                { 
                    if (queryParametersBuilder.Length > 0)
                    { 
                        queryParametersBuilder.Append('&');
                    }

                    queryParametersBuilder.Append(queryParameter).Append('=').Append(value); 
                }
            } 
 
            int? topQueryParameter = this.GetTopQueryParameter();
            if (topQueryParameter.HasValue) 
            {
                int remainingResults = topQueryParameter.Value;

                // We don't touch the top count in case of custom paging. 
                if (!this.IsCustomPaged)
                { 
                    remainingResults = topQueryParameter.Value - this.CurrentContainer.PageSize; 
                }
 
                if (remainingResults > 0)
                {
                    if (queryParametersBuilder.Length > 0)
                    { 
                        queryParametersBuilder.Append('&');
                    } 
 
                    queryParametersBuilder.Append(XmlConstants.HttpQueryStringTop).Append('=').Append(remainingResults);
                } 
            }

            if (queryParametersBuilder.Length > 0)
            { 
                queryParametersBuilder.Append('&');
            } 
 
            return queryParametersBuilder;
        } 

        /// Recursive method which builds the $expand and $select paths for the specified node.
        /// List of path segments which lead up to this node.
        /// So for example if the specified node is Orders/OrderDetails the list will contains two strings 
        /// "Orders" and "OrderDetails".
        /// The result to which the projection paths are appended as a comma separated list. 
        /// The result to which the expansion paths are appended as a comma separated list. 
        /// The node to inspect.
        /// Out parameter which is set to true if there were some explicit projections on the inspected node. 
        /// Our parameter which is set to true if there were some expansions on the inspected node.
        private void BuildProjectionAndExpansionPathsForNode(
            List parentPathSegments,
            StringBuilder projectionPaths, 
            StringBuilder expansionPaths,
            ExpandedProjectionNode expandedNode, 
            out bool foundProjections, 
            out bool foundExpansions)
        { 
            foundProjections = false;
            foundExpansions = false;

            bool foundExpansionChild = false; 
            bool foundProjectionChild = false;
            List expandedChildrenNeededToBeProjected = new List(); 
            foreach (ProjectionNode childNode in expandedNode.Nodes) 
            {
                ExpandedProjectionNode expandedChildNode = childNode as ExpandedProjectionNode; 
                if (expandedChildNode == null)
                {
                    // Explicitely project the property mentioned in this node
                    AppendProjectionOrExpansionPath(projectionPaths, parentPathSegments, childNode.PropertyName); 
                    foundProjections = true;
                } 
                else 
                {
                    foundExpansions = true; 

                    parentPathSegments.Add(expandedChildNode.PropertyName);
                    this.BuildProjectionAndExpansionPathsForNode(
                        parentPathSegments, 
                        projectionPaths,
                        expansionPaths, 
                        expandedChildNode, 
                        out foundProjectionChild,
                        out foundExpansionChild); 
                    parentPathSegments.RemoveAt(parentPathSegments.Count - 1);

                    // Add projection paths for this node if all its properties should be projected
                    if (expandedChildNode.ProjectAllProperties) 
                    {
                        if (foundProjectionChild) 
                        { 
                            // There were some projections in our children, but this node requires all properties -> project *
                            AppendProjectionOrExpansionPath(projectionPaths, parentPathSegments, childNode.PropertyName + "/*"); 
                        }
                        else
                        {
                            // There were no projections underneath this node, so we need to "project" this node 
                            // we just don't know yet if we need to project this one explicitly or if some parent will do it for us implicitly.
                            expandedChildrenNeededToBeProjected.Add(expandedChildNode); 
                        } 
                    }
 
                    foundProjections |= foundProjectionChild;

                    if (!foundExpansionChild)
                    { 
                        // If there were no expansions in children, we need to add this node to expansion list
                        AppendProjectionOrExpansionPath(expansionPaths, parentPathSegments, childNode.PropertyName); 
                    } 
                }
            } 

            if (!expandedNode.ProjectAllProperties || foundProjections)
            {
                // If we already projected some properties explicitely or this node does not want to project all properties 
                // and we have some expanded children which were not projected yet
                // we need to project those explicitely (as the other projections disable the "include all" for this node 
                // or we don't really want the "include all" anyway) 
                foreach (ExpandedProjectionNode childToProject in expandedChildrenNeededToBeProjected)
                { 
                    AppendProjectionOrExpansionPath(projectionPaths, parentPathSegments, childToProject.PropertyName);

                    // And since we're adding an explicit projection, mark us as using explicit projections
                    foundProjections = true; 
                }
            } 
        } 

        ///  
        /// Builds the string corresponding to query parameters for top level results to be put in next page link.
        /// 
        /// StringBuilder which has the query parameters in the URI query parameter format.
        private StringBuilder GetNextPageQueryParametersForExpandedContainer() 
        {
            StringBuilder queryParametersBuilder = new StringBuilder(); 
 
            ExpandedProjectionNode expandedProjectionNode = this.GetCurrentExpandedProjectionNode();
            if (expandedProjectionNode != null) 
            {
                // Build a string containing all the $expand and $select for the current node and children
                List pathSegments = new List();
                StringBuilder projectionPaths = new StringBuilder(); 
                StringBuilder expansionPaths = new StringBuilder();
                bool foundExpansions = false; 
                bool foundProjections = false; 
                this.BuildProjectionAndExpansionPathsForNode(
                    pathSegments, 
                    projectionPaths,
                    expansionPaths,
                    expandedProjectionNode,
                    out foundProjections, 
                    out foundExpansions);
 
                // In most cases the root level of the query is projected by default 
                // The only exception is if there were projections in some children
                // and we need all the properties of the root -> then project * 
                if (foundProjections && expandedProjectionNode.ProjectAllProperties)
                {
                    AppendProjectionOrExpansionPath(projectionPaths, pathSegments, "*");
                } 

                if (projectionPaths.Length > 0) 
                { 
                    if (queryParametersBuilder.Length > 0)
                    { 
                        queryParametersBuilder.Append('&');
                    }

                    queryParametersBuilder.Append("$select=").Append(projectionPaths.ToString()); 
                }
 
                if (expansionPaths.Length > 0) 
                {
                    if (queryParametersBuilder.Length > 0) 
                    {
                        queryParametersBuilder.Append('&');
                    }
 
                    queryParametersBuilder.Append("$expand=").Append(expansionPaths.ToString());
                } 
            } 

            if (queryParametersBuilder.Length > 0) 
            {
                queryParametersBuilder.Append('&');
            }
 
            return queryParametersBuilder;
        } 
 
        /// Pushes a segment from the stack of names being written.
        /// Name of property to push. 
        /// Container to push (possibly null).
        /// Calls to this method should be balanced with calls to PopSegmentName.
        /// true if a segment was push, false otherwise
        private bool PushSegment(string name, ResourceSetWrapper container) 
        {
            if (this.service.Configuration.MaxResultsPerCollection != Int32.MaxValue || 
                (container != null && container.PageSize != 0) || // Complex types have null container , paging should force a push 
                (this.requestDescription.RootProjectionNode != null &&
                 this.requestDescription.RootProjectionNode.ExpansionsSpecified)) 
            {
                if (this.segmentNames == null)
                {
                    this.segmentNames = new List(); 
                    this.segmentContainers = new List();
                    this.segmentResultCounts = new List(); 
                } 

                Debug.Assert( 
                    this.segmentContainers.Count == this.segmentNames.Count,
                    "this.segmentContainers.Count == this.segmentNames.Count -- should always be one-to-one");
                Debug.Assert(
                    this.segmentContainers.Count == this.segmentResultCounts.Count, 
                    "this.segmentContainers.Count == this.segmentResultCounts.Count -- should always be one-to-one");
                this.segmentNames.Add(name); 
                this.segmentContainers.Add(container); 
                this.segmentResultCounts.Add(0);
                Debug.Assert( 
                    this.segmentContainers.Count == this.segmentNames.Count,
                    "this.segmentContainers.Count == this.segmentNames.Count -- should always be one-to-one");
                Debug.Assert(
                    this.segmentContainers.Count == this.segmentResultCounts.Count, 
                    "this.segmentContainers.Count == this.segmentResultCounts.Count -- should always be one-to-one");
                return true; 
            } 

            return false; 
        }

        /// 
        /// Obtains the $top query parameter value. 
        /// 
        /// Integer value for $top or null otherwise. 
        private int? GetTopQueryParameter() 
        {
            String topQueryItem = this.service.OperationContext.Host.GetQueryStringItem(XmlConstants.HttpQueryStringTop); 
            if (!String.IsNullOrEmpty(topQueryItem))
            {
                return Int32.Parse(topQueryItem, System.Globalization.CultureInfo.InvariantCulture);
            } 
            else
            { 
                return null; 
            }
        } 

        /// 
        /// Builds the $skiptoken=[value,value] representation for appending to the next page link URI.
        ///  
        private abstract class SkipTokenBuilder
        { 
            /// Skip token string representation. 
            private StringBuilder skipToken;
 
            /// Constructor.
            public SkipTokenBuilder()
            {
                this.skipToken = new StringBuilder(); 
                this.skipToken.Append(XmlConstants.HttpQueryStringSkipToken).Append('=');
            } 
 
            /// Returns the string representation for $skiptoken query parameter.
            /// String representation for $skiptoken query parameter. 
            public StringBuilder GetSkipToken()
            {
                object[] skipTokenProperties = this.GetSkipTokenProperties();
 
                bool first = true;
                for (int i = 0; i < skipTokenProperties.Length; i++) 
                { 
                    object value = skipTokenProperties[i];
                    string stringValue; 

                    if (value == null)
                    {
                        stringValue = Parsing.ExpressionConstants.KeywordNull; 
                    }
                    else 
                    if (!System.Data.Services.Parsing.WebConvert.TryKeyPrimitiveToString(value, out stringValue)) 
                    {
                        throw new InvalidOperationException(Strings.Serializer_CannotConvertValue(value)); 
                    }

                    if (!first)
                    { 
                        this.skipToken.Append(',');
                    } 
 
                    this.skipToken.Append(System.Uri.EscapeDataString(stringValue));
                    first = false; 
                }

                return this.skipToken;
            } 

            /// Derived classes override this to provide the collection of values for skip token. 
            /// Array of primitive values that comprise the skip token. 
            protected abstract object[] GetSkipTokenProperties();
        } 

        /// Obtains the skip token from IExpandedResult values.
        private class SkipTokenBuilderFromExpandedResult : SkipTokenBuilder
        { 
            /// IExpandedResult to lookup for skip token values.
            private IExpandedResult skipTokenExpandedResult; 
 
            /// Number of values in skip token.
            private int skipTokenExpressionCount; 

            /// Constructor.
            /// IExpandedResult to lookup for skip token values.
            /// Number of values in skip token. 
            public SkipTokenBuilderFromExpandedResult(IExpandedResult skipTokenExpandedResult, int skipTokenExpressionCount)
                : base() 
            { 
                this.skipTokenExpandedResult = skipTokenExpandedResult;
                this.skipTokenExpressionCount = skipTokenExpressionCount; 
            }

            /// Obtains skip token values by looking up IExpandedResult.
            /// Array of primitive values that comprise the skip token. 
            protected override object[] GetSkipTokenProperties()
            { 
                object[] values = new object[this.skipTokenExpressionCount]; 

                for (int i = 0; i < this.skipTokenExpressionCount; i++) 
                {
                    String keyName = XmlConstants.SkipTokenPropertyPrefix + i.ToString(System.Globalization.CultureInfo.InvariantCulture);
                    object value = this.skipTokenExpandedResult.GetExpandedPropertyValue(keyName);
                    if (value == DBNull.Value) 
                    {
                        value = null; 
                    } 

                    values[i] = value; 
                }

                return values;
            } 
        }
 
        /// Obtains the skip token by reading properties directly from an object. 
        private class SkipTokenBuilderFromProperties : SkipTokenBuilder
        { 
            /// Object to read skip token values from.
            private object element;

            /// Collection of properties that comprise the skip token. 
            private ICollection properties;
 
            /// Current provider. 
            private DataServiceProviderWrapper provider;
 
            /// Constructor.
            /// Object to read skip token values from.
            /// Current provider.
            /// Collection of properties that comprise the skip token. 
            public SkipTokenBuilderFromProperties(object element, DataServiceProviderWrapper provider, ICollection properties)
                : base() 
            { 
                this.element = element;
                this.provider = provider; 
                this.properties = properties;
            }

            /// Obtains skip token values by reading properties directly from the last object. 
            /// Array of primitive values that comprise the skip token.
            protected override object[] GetSkipTokenProperties() 
            { 
                object[] values = new object[this.properties.Count];
 
                int propertyIndex = 0;
                foreach (ResourceProperty property in this.properties)
                {
                    object value = WebUtil.GetPropertyValue(this.provider, this.element, null, property, null); 
                    if (value == DBNull.Value)
                    { 
                        value = null; 
                    }
 
                    values[propertyIndex++] = value;
                }

                return values; 
            }
        } 
 
        /// Provides the skip token obtained from the custom paging provider.
        private class SkipTokenBuilderFromCustomPaging : SkipTokenBuilder 
        {
            /// Skip token obtained from custom paging provider.
            private object[] lastTokenValue;
 
            /// Constructor.
            /// Skip token obtained from custom paging provider. 
            public SkipTokenBuilderFromCustomPaging(object[] lastTokenValue) 
                : base()
            { 
                this.lastTokenValue = lastTokenValue;
            }

            /// Provides the skip token values that were obtained from custom paging provider. 
            /// Array of primitive values that comprise the skip token.
            protected override object[] GetSkipTokenProperties() 
            { 
                return this.lastTokenValue;
            } 
        }
    }
}

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
//---------------------------------------------------------------------- 
// 
//      Copyright (c) Microsoft Corporation.  All rights reserved.
// 
//  
//      An abstract base serializer for various serializers
//  
// 
// @owner  [....]
//--------------------------------------------------------------------- 

namespace System.Data.Services.Serializers
{
    #region Namespaces. 

    using System; 
    using System.Collections; 
    using System.Collections.Generic;
    using System.Data.Services; 
    using System.Data.Services.Providers;
    using System.Diagnostics;
    using System.Text;
    using System.Data.Services.Internal; 

    #endregion Namespaces. 
 
    /// Abstract base class for all serializers.
    internal abstract class Serializer : IExceptionWriter 
    {
        #region Private fields.

        /// Maximum recursion limit on serializers. 
        private const int RecursionLimit = 100;
 
        ///  
        /// These query parameters can be copied for each next page link.
        /// Don't need to copy $skiptoken, $skip and $top because they are calculated every time. 
        /// 
        private static readonly String[] NextPageQueryParametersToCopy =
        {
            XmlConstants.HttpQueryStringFilter, 
            XmlConstants.HttpQueryStringExpand,
            XmlConstants.HttpQueryStringOrderBy, 
            XmlConstants.HttpQueryStringInlineCount, 
            XmlConstants.HttpQueryStringSelect
        }; 

        /// Base URI from which resources should be resolved.
        private readonly Uri absoluteServiceUri;
 
        /// Data provider from which metadata should be gathered.
        private readonly string httpETagHeaderValue; 
 
        /// Data provider from which metadata should be gathered.
        private readonly IDataService service; 

        /// Description for the requested results.
        private readonly RequestDescription requestDescription;
 
        /// Collection of complex types, used for cycle detection.
        private HashSet complexTypeCollection; 
 
        /// Resolved segment containers.
        private List segmentContainers; 

        /// Segment names.
        private List segmentNames;
 
        /// Result counts for segments.
        private List segmentResultCounts; 
 
        /// Depth of recursion.
        private int recursionDepth; 

        /// Current skip token object for custom paging.
        private object[] currentSkipTokenForCustomPaging;
 
        #endregion Private fields.
 
        /// Initializes a new base Serializer, ready to write out a description. 
        /// Description for the requested results.
        /// Base URI from which resources should be resolved. 
        /// Service with configuration and provider from which metadata should be gathered.
        /// HTTP ETag header value.
        internal Serializer(RequestDescription requestDescription, Uri absoluteServiceUri, IDataService service, string httpETagHeaderValue)
        { 
            Debug.Assert(requestDescription != null, "requestDescription != null");
            Debug.Assert(absoluteServiceUri != null, "absoluteServiceUri != null"); 
            Debug.Assert(service != null, "service != null"); 

            this.requestDescription = requestDescription; 
            this.absoluteServiceUri = absoluteServiceUri;
            this.service = service;
            this.httpETagHeaderValue = httpETagHeaderValue;
        } 

        /// Container for the resource being serialized (possibly null). 
        protected ResourceSetWrapper CurrentContainer 
        {
            get 
            {
                if (this.segmentContainers == null || this.segmentContainers.Count == 0)
                {
                    return this.requestDescription.LastSegmentInfo.TargetContainer; 
                }
                else 
                { 
                    return this.segmentContainers[this.segmentContainers.Count - 1];
                } 
            }
        }

        /// Is current container the root container. 
        protected bool IsRootContainer
        { 
            get 
            {
                return (this.segmentContainers == null || this.segmentContainers.Count == 1); 
            }
        }

        ///  
        /// Gets the Data provider from which metadata should be gathered.
        ///  
        protected DataServiceProviderWrapper Provider 
        {
            [DebuggerStepThrough] 
            get { return this.service.Provider; }
        }

        ///  
        /// Gets the Data service from which metadata should be gathered.
        ///  
        protected IDataService Service 
        {
            [DebuggerStepThrough] 
            get { return this.service; }
        }

        /// Gets the absolute URI to the service. 
        protected Uri AbsoluteServiceUri
        { 
            [DebuggerStepThrough] 
            get { return this.absoluteServiceUri; }
        } 

        /// 
        /// Gets the RequestDescription for the request that is getting serialized.
        ///  
        protected RequestDescription RequestDescription
        { 
            [DebuggerStepThrough] 
            get
            { 
                return this.requestDescription;
            }
        }
 
        /// Are we using custom paging?
        protected bool IsCustomPaged 
        { 
            get
            { 
                return this.service.PagingProvider.IsCustomPagedForSerialization;
            }
        }
 
        /// Serializes exception information.
        /// Description of exception to serialize. 
        public abstract void WriteException(HandleExceptionArgs args); 

        ///  
        /// Gets the uri given the list of resource properties. This logic must be the same across all
        /// serializers. Hence putting this in a util class
        /// 
        /// instance of the resource type whose properties needs to be returned 
        /// Provider from which resource was obtained.
        /// Container for the resource. 
        /// Base URI from which resources should be resolved. 
        /// uri for the given resource
        internal static Uri GetUri(object resource, DataServiceProviderWrapper provider, ResourceSetWrapper container, Uri absoluteServiceUri) 
        {
            Debug.Assert(container != null, "container != null");
            string objectKey = GetObjectKey(resource, provider, container.Name);
            return RequestUriProcessor.AppendEscapedSegment(absoluteServiceUri, objectKey); 
        }
 
        ///  
        /// Appends the given entry to the given uri
        ///  
        /// uri to which the entry needs to be appended
        /// entry which gets appended to the given uri
        /// new uri with the entry appended to the given uri
        internal static Uri AppendEntryToUri(Uri currentUri, string entry) 
        {
            return RequestUriProcessor.AppendUnescapedSegment(currentUri, entry); 
        } 

        ///  
        /// Handles the complete serialization for the specified .
        /// 
        /// Query results to enumerate.
        /// Whether  was succesfully advanced to the first element. 
        /// 
        ///  should correspond to the RequestQuery of the 
        /// RequestDescription object passed while constructing this serializer 
        /// We allow the results to be passed in
        /// to let the query be executed earlier than at result-writing time, which 
        /// helps detect data and query errors where they can be better handled.
        /// 
        internal void WriteRequest(IEnumerator queryResults, bool hasMoved)
        { 
            Debug.Assert(this.requestDescription.RequestEnumerable != null, "this.requestDescription.RequestEnumerable != null");
            Debug.Assert(queryResults != null, "queryResults != null"); 
            IExpandedResult expanded = queryResults as IExpandedResult; 

            if (this.requestDescription.LinkUri) 
            {
                bool needPop = this.PushSegmentForRoot();
                if (this.requestDescription.IsSingleResult)
                { 
                    this.WriteLink(queryResults.Current);
                    if (queryResults.MoveNext()) 
                    { 
                        throw new InvalidOperationException(Strings.SingleResourceExpected);
                    } 
                }
                else
                {
                    this.WriteLinkCollection(queryResults, hasMoved); 
                }
 
                this.PopSegmentName(needPop); 
            }
            else if (this.requestDescription.IsSingleResult) 
            {
                Debug.Assert(hasMoved == true, "hasMoved == true");
                this.WriteTopLevelElement(expanded, queryResults.Current);
                if (queryResults.MoveNext()) 
                {
                    throw new InvalidOperationException(Strings.SingleResourceExpected); 
                } 
            }
            else 
            {
                this.WriteTopLevelElements(expanded, queryResults, hasMoved);
            }
 
            this.Flush();
        } 
 
        /// Gets the expandable value for the specified object.
        /// underlying data source instance. 
        /// Expanded properties for the result, possibly null.
        /// Object with value to retrieve.
        /// Property for which value will be retrieved.
        /// The property value. 
        protected static object GetExpandedProperty(DataServiceProviderWrapper provider, IExpandedResult expanded, object customObject, ResourceProperty property)
        { 
            Debug.Assert(property != null, "property != null"); 
            if (expanded == null)
            { 
                return WebUtil.GetPropertyValue(provider, customObject, null, property, null);
            }
            else
            { 
                // We may end up projecting null as a value of ResourceSetReference property. This can in theory break
                //   the serializers as they expect a non-null (possibly empty) IEnumerable instead. But note that 
                //   if we project null into the expanded property, we also project null into the ExpandedElement property 
                //   and thus the serializers should recognize this value as null and don't try to expand its properties.
                Debug.Assert( 
                    expanded.ExpandedElement != null,
                    "We should not be accessing expanded properties on null resource.");
                return expanded.GetExpandedPropertyValue(property.Name);
            } 
        }
 
        /// Gets the expanded element for the specified expanded result. 
        /// The expanded result to process.
        /// The expanded element. 
        protected static object GetExpandedElement(IExpandedResult expanded)
        {
            Debug.Assert(expanded != null, "expanded != null");
            return expanded.ExpandedElement; 
        }
 
        /// Flushes the writer to the underlying stream. 
        protected abstract void Flush();
 
        /// Writes a single top-level element.
        /// Expanded properties for the result.
        /// Element to write, possibly null.
        protected abstract void WriteTopLevelElement(IExpandedResult expanded, object element); 

        /// Writes multiple top-level elements, possibly none. 
        /// Expanded properties for the result. 
        /// Result elements.
        /// Whether  was succesfully advanced to the first element. 
        protected abstract void WriteTopLevelElements(IExpandedResult expanded, IEnumerator elements, bool hasMoved);

        /// 
        /// Write out the entry count 
        /// 
        protected abstract void WriteRowCount(); 
 
        /// 
        /// Write out the uri for the given element 
        /// 
        /// element whose uri needs to be written out.
        protected abstract void WriteLink(object element);
 
        /// 
        /// Write out the uri for the given elements 
        ///  
        /// elements whose uri need to be writtne out
        /// the current state of the enumerator. 
        protected abstract void WriteLinkCollection(IEnumerator elements, bool hasMoved);

        /// 
        /// Adds the given object instance to complex type collection 
        /// 
        /// instance to be added 
        /// true, if it got added successfully 
        protected bool AddToComplexTypeCollection(object complexTypeInstance)
        { 
            if (this.complexTypeCollection == null)
            {
                this.complexTypeCollection = new HashSet(ReferenceEqualityComparer.Instance);
            } 

            return this.complexTypeCollection.Add(complexTypeInstance); 
        } 

        ///  
        /// Gets the skip token object contained in the expanded result for standard paging.
        /// 
        /// Current expanded result.
        /// Skip token object if any. 
        protected IExpandedResult GetSkipToken(IExpandedResult expanded)
        { 
            if (expanded != null && !this.IsCustomPaged && !this.RequestDescription.IsRequestForEnumServiceOperation) 
            {
                return expanded.GetExpandedPropertyValue(XmlConstants.HttpQueryStringSkipToken) as IExpandedResult; 
            }

            return null;
        } 

        ///  
        /// Obtains the URI for the link for next page in string format 
        /// 
        /// Last object serialized to be used for generating $skiptoken 
        /// The  of the $skiptoken property of object corresponding to last serialized object
        /// Absolute response URI
        /// URI for the link for next page
        protected String GetNextLinkUri(object lastObject, IExpandedResult skipTokenExpandedResult, Uri absoluteUri) 
        {
            UriBuilder builder = new UriBuilder(absoluteUri); 
            SkipTokenBuilder skipTokenBuilder = null; 

            if (this.IsRootContainer) 
            {
                if (!this.IsCustomPaged)
                {
                    if (skipTokenExpandedResult != null) 
                    {
                        skipTokenBuilder = new SkipTokenBuilderFromExpandedResult(skipTokenExpandedResult, this.RequestDescription.SkipTokenExpressionCount); 
                    } 
                    else
                    { 
                        Debug.Assert(this.RequestDescription.SkipTokenProperties != null, "Must have skip token properties collection");
                        Debug.Assert(this.RequestDescription.SkipTokenProperties.Count > 0, "Must have some valid ordered properties in the skip token properties collection");
                        skipTokenBuilder = new SkipTokenBuilderFromProperties(lastObject, this.Provider, this.RequestDescription.SkipTokenProperties);
                    } 
                }
                else 
                { 
                    Debug.Assert(this.currentSkipTokenForCustomPaging != null, "Must have obtained the skip token for custom paging.");
                    skipTokenBuilder = new SkipTokenBuilderFromCustomPaging(this.currentSkipTokenForCustomPaging); 
                }

                builder.Query = this.GetNextPageQueryParametersForRootContainer().Append(skipTokenBuilder.GetSkipToken()).ToString();
            } 
            else
            { 
                if (!this.IsCustomPaged) 
                {
                    // Internal results 
                    skipTokenBuilder = new SkipTokenBuilderFromProperties(lastObject, this.Provider, this.CurrentContainer.ResourceType.KeyProperties);
                }
                else
                { 
                    Debug.Assert(this.currentSkipTokenForCustomPaging != null, "Must have obtained the skip token for custom paging.");
                    skipTokenBuilder = new SkipTokenBuilderFromCustomPaging(this.currentSkipTokenForCustomPaging); 
                } 

                builder.Query = this.GetNextPageQueryParametersForExpandedContainer().Append(skipTokenBuilder.GetSkipToken()).ToString(); 
            }

            return builder.Uri.AbsoluteUri;
        } 

        /// Is next page link needs to be appended to the feed 
        /// Current result enumerator. 
        /// true if the feed must have a next page link
        protected bool NeedNextPageLink(IEnumerator enumerator) 
        {
            // For open types, current container could be null
            if (this.CurrentContainer != null && !this.RequestDescription.IsRequestForEnumServiceOperation)
            { 
                if (this.IsCustomPaged)
                { 
                    this.currentSkipTokenForCustomPaging = 
                        this.service.PagingProvider.PagingProviderInterface.GetContinuationToken(BasicExpandProvider.ExpandedEnumerator.UnwrapEnumerator(enumerator));
                    Debug.Assert( 
                            this.RequestDescription.ResponseVersion != RequestDescription.DataServiceDefaultResponseVersion,
                            "If custom paging is enabled, our response should be 2.0 and beyond.");

                    return this.currentSkipTokenForCustomPaging != null && this.currentSkipTokenForCustomPaging.Length > 0; 
                }
                else 
                { 
                    int pageSize = this.CurrentContainer.PageSize;
 
                    if (pageSize != 0 && this.RequestDescription.ResponseVersion != RequestDescription.DataServiceDefaultResponseVersion)
                    {
                        // For the root segment, if the $top parameter value is less than or equal to page size then we
                        // don't need to send the next page link. 
                        if (this.segmentResultCounts.Count == 1)
                        { 
                            int? topQueryParameter = this.GetTopQueryParameter(); 

                            if (topQueryParameter.HasValue) 
                            {
                                Debug.Assert(topQueryParameter.Value >= this.segmentResultCounts[this.segmentResultCounts.Count - 1], "$top must be the upper limits of the number of results returned.");
                                if (topQueryParameter.Value <= pageSize)
                                { 
                                    return false;
                                } 
                            } 
                        }
 
                        return this.segmentResultCounts[this.segmentResultCounts.Count - 1] == pageSize;
                    }
                }
            } 

            return false; 
        } 

        /// Pushes a segment for the root of the tree being written out. 
        /// Name of open property.
        /// Resulved type of open property.
        /// Calls to this method should be balanced with calls to PopSegmentName.
        /// true if segment was pushed, false otherwise 
        protected bool PushSegmentForOpenProperty(string propertyName, ResourceType propertyResourceType)
        { 
            Debug.Assert(propertyName != null, "propertyName != null"); 
            Debug.Assert(propertyResourceType != null, "propertyResourceType != null");
            ResourceSetWrapper container = null; 
            if (propertyResourceType.ResourceTypeKind == ResourceTypeKind.EntityType)
            {
                // Open navigation properties are not supported on OpenTypes.
                throw DataServiceException.CreateBadRequestError(Strings.OpenNavigationPropertiesNotSupportedOnOpenTypes(propertyName)); 
            }
 
            return this.PushSegment(propertyName, container); 
        }
 
        /// Increments the result count for the current segment, throws if exceeds the limit.
        protected void IncrementSegmentResultCount()
        {
            if (this.segmentResultCounts != null) 
            {
                Debug.Assert(this.segmentResultCounts.Count > 0, "this.segmentResultCounts.Count > 0 -- otherwise we didn't PushSegmentForRoot"); 
                int max = this.service.Configuration.MaxResultsPerCollection; 

                if (!this.IsCustomPaged) 
                {
                    // For Open types, current container could be null, even though MaxResultsPerCollection has been set
                    // set we need to check for container before we try to assume page size, also open types do not have
                    // page sizes so we can safely ignore this check here 
                    if (this.CurrentContainer != null && this.CurrentContainer.PageSize != 0)
                    { 
                        Debug.Assert(max == Int32.MaxValue, "Either page size or max result count can be set, but not both"); 
                        max = this.CurrentContainer.PageSize;
                    } 
                }

                if (max != Int32.MaxValue)
                { 
                    int count = this.segmentResultCounts[this.segmentResultCounts.Count - 1];
                    checked 
                    { 
                        count++;
                    } 

                    if (count > max)
                    {
                        throw DataServiceException.CreateBadRequestError(Strings.Serializer_ResultsExceedMax(max)); 
                    }
 
                    this.segmentResultCounts[this.segmentResultCounts.Count - 1] = count; 
                }
            } 
        }

        /// Pushes a segment from the stack of names being written.
        /// Property to push. 
        /// Calls to this method should be balanced with calls to PopSegmentName.
        /// true if a segment was pushed, false otherwise 
        protected bool PushSegmentForProperty(ResourceProperty property) 
        {
            Debug.Assert(property != null, "property != null"); 
            ResourceSetWrapper current = null;
            if ((property.Kind & (ResourcePropertyKind.ResourceReference | ResourcePropertyKind.ResourceSetReference)) != 0)
            {
                current = this.CurrentContainer; 
                if (current != null)
                { 
                    current = this.service.Provider.GetContainer(current, current.ResourceType, property); 
                }
            } 

            return this.PushSegment(property.Name, current);
        }
 
        /// Pushes a segment for the root of the tree being written out.
        /// Calls to this method should be balanced with calls to PopSegmentName. 
        /// true if the segment was pushed, false otherwise 
        protected bool PushSegmentForRoot()
        { 
            return this.PushSegment(this.RequestDescription.ContainerName, this.CurrentContainer);
        }

        /// Pops a segment name from the stack of names being written. 
        /// Is a pop required. Only true if last push was successful
        /// Calls to this method should be balanced with previous calls to PushSegmentName. 
        protected void PopSegmentName(bool needPop) 
        {
            if (this.segmentNames != null && needPop) 
            {
                Debug.Assert(this.segmentNames.Count > 0, "this.segmentNames.Count > 0");
                this.segmentNames.RemoveAt(this.segmentNames.Count - 1);
                this.segmentContainers.RemoveAt(this.segmentContainers.Count - 1); 
                this.segmentResultCounts.RemoveAt(this.segmentResultCounts.Count - 1);
                Debug.Assert( 
                    this.segmentContainers.Count == this.segmentNames.Count, 
                    "this.segmentContainers.Count == this.segmentNames.Count -- should always be one-to-one");
                Debug.Assert( 
                    this.segmentContainers.Count == this.segmentResultCounts.Count,
                    "this.segmentContainers.Count == this.segmentResultCounts.Count -- should always be one-to-one");
            }
        } 

        /// Marks the fact that a recursive method was entered, and checks that the depth is allowed. 
        protected void RecurseEnter() 
        {
            WebUtil.RecurseEnter(RecursionLimit, ref this.recursionDepth); 
        }

        /// Marks the fact that a recursive method is leaving.
        protected void RecurseLeave() 
        {
            WebUtil.RecurseLeave(ref this.recursionDepth); 
        } 

        /// Returns a clone of the segment names and containers trackd at this moment. 
        /// A clone of the segment names and containers tracked at this moment; possibly null.
        protected object SaveSegmentNames()
        {
            if (this.segmentNames == null) 
            {
                return null; 
            } 
            else
            { 
                return new object[3]
                {
                    new List(this.segmentNames),
                    new List(this.segmentContainers), 
                    new List(this.segmentResultCounts)
                }; 
            } 
        }
 
        /// Restores the segment names saved through .
        /// Value returned from a previous call to .
        protected void RestoreSegmentNames(object savedSegmentNames)
        { 
            object[] savedLists = (object[])savedSegmentNames;
            if (savedLists == null) 
            { 
                this.segmentNames = null;
                this.segmentContainers = null; 
                this.segmentResultCounts = null;
            }
            else
            { 
                this.segmentNames = (List)savedLists[0];
                this.segmentContainers = (List)savedLists[1]; 
                this.segmentResultCounts = (List)savedLists[2]; 
            }
        } 

        /// 
        /// Remove the given object instance from the complex type collection
        ///  
        /// instance to be removed
        protected void RemoveFromComplexTypeCollection(object complexTypeInstance) 
        { 
            Debug.Assert(this.complexTypeCollection != null, "this.complexTypeCollection != null");
            Debug.Assert(this.complexTypeCollection.Contains(complexTypeInstance), "this.complexTypeCollection.Contains(complexTypeInstance)"); 

            this.complexTypeCollection.Remove(complexTypeInstance);
        }
 
        /// Checks whether the property with the specified name should be expanded in-line.
        /// Name of property to consider for expansion. 
        /// true if the segment should be expanded; false otherwise. 
        protected bool ShouldExpandSegment(string name)
        { 
            Debug.Assert(name != null, "name != null");

            if (this.segmentNames == null)
            { 
                return false;
            } 
 
            if (this.requestDescription.RootProjectionNode != null)
            { 
                if (this.requestDescription.RootProjectionNode.UseExpandPathsForSerialization &&
                    this.requestDescription.RootProjectionNode.ExpandPaths != null)
                {
                    // We need to use the old ExpandPaths to determine which segments to expand 
                    //   since the IExpandProvider might have modified this collection.
                    for (int i = 0; i < this.requestDescription.RootProjectionNode.ExpandPaths.Count; i++) 
                    { 
                        List expandPath = this.requestDescription.RootProjectionNode.ExpandPaths[i];
                        if (expandPath.Count < this.segmentNames.Count) 
                        {
                            continue;
                        }
 
                        // We start off at '1' for segment names because the first one is the
                        // "this" in the query (/Customers?$expand=Orders doesn't include "Customers"). 
                        bool matchFound = true; 
                        for (int j = 1; j < this.segmentNames.Count; j++)
                        { 
                            if (expandPath[j - 1].Name != this.segmentNames[j])
                            {
                                matchFound = false;
                                break; 
                            }
                        } 
 
                        if (matchFound && expandPath[this.segmentNames.Count - 1].Name == name)
                        { 
                            return true;
                        }
                    }
                } 
                else
                { 
                    // We can use the new tree of expanded nodes to determine the expansions. 
                    // So find the expanded node on which we are now.
                    ExpandedProjectionNode expandedNode = this.GetCurrentExpandedProjectionNode(); 
                    if (expandedNode != null)
                    {
                        // And then if that node contains a child node of the specified name
                        //   and that child is also an expanded node, we should expand it. 
                        ProjectionNode lastNode = expandedNode.FindNode(name);
                        if (lastNode != null && lastNode is ExpandedProjectionNode) 
                        { 
                            return true;
                        } 
                    }
                }
            }
 
            return false;
        } 
 
        /// Returns a list of projection segments defined for the current segment.
        /// List of  describing projections for the current segment. 
        /// If this method returns null it means no projections are to be applied and the entire resource
        /// for the current segment should be serialized. If it returns non-null only the properties described
        /// by the returned projection segments should be serialized.
        protected IEnumerable GetProjections() 
        {
            ExpandedProjectionNode expandedProjectionNode = this.GetCurrentExpandedProjectionNode(); 
            if (expandedProjectionNode == null || expandedProjectionNode.ProjectAllProperties) 
            {
                return null; 
            }
            else
            {
                return expandedProjectionNode.Nodes; 
            }
        } 
 
        /// 
        /// Returns the ETag value from the host response header 
        /// 
        /// resource whose etag value gets to be returned
        /// returns the etag value for the given resource
        protected string GetETagValue(object resource) 
        {
            // this.httpETagHeaderValue is the etag value which got computed for writing the etag in the response 
            // headers. The etag response header only gets written out in certain scenarios, whereas we always 
            // write etag in the response payload, if the type has etag properties. So just checking here is the
            // etag has already been computed, and if yes, returning that, otherwise computing the etag. 
            if (!String.IsNullOrEmpty(this.httpETagHeaderValue))
            {
                return this.httpETagHeaderValue;
            } 
            else
            { 
                Debug.Assert(this.CurrentContainer != null, "this.CurrentContainer != null"); 
                return WebUtil.GetETagValue(this.service, resource, this.CurrentContainer);
            } 
        }

        /// Returns the key for the given resource.
        /// Resource for which key value needs to be returned. 
        /// Specific provider from which resource was obtained.
        /// name of the entity container that the resource belongs to 
        /// Key for the given resource, with values encoded for use in a URI. 
        private static string GetObjectKey(object resource, DataServiceProviderWrapper provider, string containerName)
        { 
            Debug.Assert(resource != null, "resource != null");
            Debug.Assert(provider != null, "provider != null");
            Debug.Assert(!String.IsNullOrEmpty(containerName), "container name must be specified");
 
            StringBuilder resultBuilder = new StringBuilder();
            resultBuilder.Append(containerName); 
            resultBuilder.Append('('); 
            ResourceType resourceType = WebUtil.GetNonPrimitiveResourceType(provider, resource);
            Debug.Assert(resourceType != null, "resourceType != null"); 
            IList keyProperties = resourceType.KeyProperties;
            Debug.Assert(keyProperties.Count != 0, "every resource type must have a key");
            for (int i = 0; i < keyProperties.Count; i++)
            { 
                ResourceProperty property = keyProperties[i];
                Debug.Assert(property.IsOfKind(ResourcePropertyKind.Key), "must be key property"); 
 
                object keyValue = WebUtil.GetPropertyValue(provider, resource, resourceType, property, null);
                if (keyValue == null) 
                {
                    // null keys not supported.
                    throw new InvalidOperationException(Strings.Serializer_NullKeysAreNotSupported(property.Name));
                } 

                if (i == 0) 
                { 
                    if (keyProperties.Count != 1)
                    { 
                        resultBuilder.Append(property.Name);
                        resultBuilder.Append('=');
                    }
                } 
                else
                { 
                    resultBuilder.Append(','); 
                    resultBuilder.Append(property.Name);
                    resultBuilder.Append('='); 
                }

                string keyValueText;
                if (!System.Data.Services.Parsing.WebConvert.TryKeyPrimitiveToString(keyValue, out keyValueText)) 
                {
                    throw new InvalidOperationException(Strings.Serializer_CannotConvertValue(keyValue)); 
                } 

                Debug.Assert(keyValueText != null, "keyValueText != null - otherwise TryKeyPrimitiveToString returned true and null value"); 
                resultBuilder.Append(System.Uri.EscapeDataString(keyValueText));
            }

            resultBuilder.Append(')'); 
            return resultBuilder.ToString();
        } 
 
        /// Helper method to append a path to the $expand or $select path list.
        /// The  to which to append the path. 
        /// The segments of the path up to the last segment.
        /// The last segment of the path.
        private static void AppendProjectionOrExpansionPath(StringBuilder pathsBuilder, List parentPathSegments, string lastPathSegment)
        { 
            if (pathsBuilder.Length != 0)
            { 
                pathsBuilder.Append(','); 
            }
 
            foreach (string parentPathSegment in parentPathSegments)
            {
                pathsBuilder.Append(parentPathSegment).Append('/');
            } 

            pathsBuilder.Append(lastPathSegment); 
        } 

        /// Finds the  node which describes the current segment. 
        /// The  which describes the current segment, or null
        /// if no such node is available.
        private ExpandedProjectionNode GetCurrentExpandedProjectionNode()
        { 
            ExpandedProjectionNode expandedProjectionNode = this.RequestDescription.RootProjectionNode;
            if (expandedProjectionNode == null) 
            { 
                return null;
            } 

            if (this.segmentNames != null)
            {
                // We start off at '1' for segment names because the first one is the 
                // "this" in the query and projection segments don't have that (the root is the "this")
                for (int i = 1; i < this.segmentNames.Count; i++) 
                { 
                    ProjectionNode projectionNode = expandedProjectionNode.FindNode(this.segmentNames[i]);
                    if (projectionNode == null) 
                    {
                        // If we don't have a projection node, report everything (complex types for example).
                        return null;
                    } 

                    Debug.Assert( 
                        projectionNode is ExpandedProjectionNode, 
                        "We have a pushed segment on the serialization stack which is not backed by expanded node in the query definition.");
                    expandedProjectionNode = (ExpandedProjectionNode)projectionNode; 
                }
            }

            return expandedProjectionNode; 
        }
 
        ///  
        /// Builds the string corresponding to query parameters for top level results to be put in next page link.
        ///  
        /// StringBuilder which has the query parameters in the URI query parameter format.
        private StringBuilder GetNextPageQueryParametersForRootContainer()
        {
            StringBuilder queryParametersBuilder = new StringBuilder(); 

            // Handle service operation parameters 
            if (this.RequestDescription.SegmentInfos[0].TargetSource == RequestTargetSource.ServiceOperation) 
            {
                foreach (var parameter in this.RequestDescription.SegmentInfos[0].Operation.Parameters) 
                {
                    if (queryParametersBuilder.Length > 0)
                    {
                        queryParametersBuilder.Append('&'); 
                    }
 
                    queryParametersBuilder.Append(parameter.Name).Append('='); 
                    queryParametersBuilder.Append(this.service.OperationContext.Host.GetQueryStringItem(parameter.Name));
                } 
            }

            foreach (String queryParameter in Serializer.NextPageQueryParametersToCopy)
            { 
                String value = this.service.OperationContext.Host.GetQueryStringItem(queryParameter);
                if (!String.IsNullOrEmpty(value)) 
                { 
                    if (queryParametersBuilder.Length > 0)
                    { 
                        queryParametersBuilder.Append('&');
                    }

                    queryParametersBuilder.Append(queryParameter).Append('=').Append(value); 
                }
            } 
 
            int? topQueryParameter = this.GetTopQueryParameter();
            if (topQueryParameter.HasValue) 
            {
                int remainingResults = topQueryParameter.Value;

                // We don't touch the top count in case of custom paging. 
                if (!this.IsCustomPaged)
                { 
                    remainingResults = topQueryParameter.Value - this.CurrentContainer.PageSize; 
                }
 
                if (remainingResults > 0)
                {
                    if (queryParametersBuilder.Length > 0)
                    { 
                        queryParametersBuilder.Append('&');
                    } 
 
                    queryParametersBuilder.Append(XmlConstants.HttpQueryStringTop).Append('=').Append(remainingResults);
                } 
            }

            if (queryParametersBuilder.Length > 0)
            { 
                queryParametersBuilder.Append('&');
            } 
 
            return queryParametersBuilder;
        } 

        /// Recursive method which builds the $expand and $select paths for the specified node.
        /// List of path segments which lead up to this node.
        /// So for example if the specified node is Orders/OrderDetails the list will contains two strings 
        /// "Orders" and "OrderDetails".
        /// The result to which the projection paths are appended as a comma separated list. 
        /// The result to which the expansion paths are appended as a comma separated list. 
        /// The node to inspect.
        /// Out parameter which is set to true if there were some explicit projections on the inspected node. 
        /// Our parameter which is set to true if there were some expansions on the inspected node.
        private void BuildProjectionAndExpansionPathsForNode(
            List parentPathSegments,
            StringBuilder projectionPaths, 
            StringBuilder expansionPaths,
            ExpandedProjectionNode expandedNode, 
            out bool foundProjections, 
            out bool foundExpansions)
        { 
            foundProjections = false;
            foundExpansions = false;

            bool foundExpansionChild = false; 
            bool foundProjectionChild = false;
            List expandedChildrenNeededToBeProjected = new List(); 
            foreach (ProjectionNode childNode in expandedNode.Nodes) 
            {
                ExpandedProjectionNode expandedChildNode = childNode as ExpandedProjectionNode; 
                if (expandedChildNode == null)
                {
                    // Explicitely project the property mentioned in this node
                    AppendProjectionOrExpansionPath(projectionPaths, parentPathSegments, childNode.PropertyName); 
                    foundProjections = true;
                } 
                else 
                {
                    foundExpansions = true; 

                    parentPathSegments.Add(expandedChildNode.PropertyName);
                    this.BuildProjectionAndExpansionPathsForNode(
                        parentPathSegments, 
                        projectionPaths,
                        expansionPaths, 
                        expandedChildNode, 
                        out foundProjectionChild,
                        out foundExpansionChild); 
                    parentPathSegments.RemoveAt(parentPathSegments.Count - 1);

                    // Add projection paths for this node if all its properties should be projected
                    if (expandedChildNode.ProjectAllProperties) 
                    {
                        if (foundProjectionChild) 
                        { 
                            // There were some projections in our children, but this node requires all properties -> project *
                            AppendProjectionOrExpansionPath(projectionPaths, parentPathSegments, childNode.PropertyName + "/*"); 
                        }
                        else
                        {
                            // There were no projections underneath this node, so we need to "project" this node 
                            // we just don't know yet if we need to project this one explicitly or if some parent will do it for us implicitly.
                            expandedChildrenNeededToBeProjected.Add(expandedChildNode); 
                        } 
                    }
 
                    foundProjections |= foundProjectionChild;

                    if (!foundExpansionChild)
                    { 
                        // If there were no expansions in children, we need to add this node to expansion list
                        AppendProjectionOrExpansionPath(expansionPaths, parentPathSegments, childNode.PropertyName); 
                    } 
                }
            } 

            if (!expandedNode.ProjectAllProperties || foundProjections)
            {
                // If we already projected some properties explicitely or this node does not want to project all properties 
                // and we have some expanded children which were not projected yet
                // we need to project those explicitely (as the other projections disable the "include all" for this node 
                // or we don't really want the "include all" anyway) 
                foreach (ExpandedProjectionNode childToProject in expandedChildrenNeededToBeProjected)
                { 
                    AppendProjectionOrExpansionPath(projectionPaths, parentPathSegments, childToProject.PropertyName);

                    // And since we're adding an explicit projection, mark us as using explicit projections
                    foundProjections = true; 
                }
            } 
        } 

        ///  
        /// Builds the string corresponding to query parameters for top level results to be put in next page link.
        /// 
        /// StringBuilder which has the query parameters in the URI query parameter format.
        private StringBuilder GetNextPageQueryParametersForExpandedContainer() 
        {
            StringBuilder queryParametersBuilder = new StringBuilder(); 
 
            ExpandedProjectionNode expandedProjectionNode = this.GetCurrentExpandedProjectionNode();
            if (expandedProjectionNode != null) 
            {
                // Build a string containing all the $expand and $select for the current node and children
                List pathSegments = new List();
                StringBuilder projectionPaths = new StringBuilder(); 
                StringBuilder expansionPaths = new StringBuilder();
                bool foundExpansions = false; 
                bool foundProjections = false; 
                this.BuildProjectionAndExpansionPathsForNode(
                    pathSegments, 
                    projectionPaths,
                    expansionPaths,
                    expandedProjectionNode,
                    out foundProjections, 
                    out foundExpansions);
 
                // In most cases the root level of the query is projected by default 
                // The only exception is if there were projections in some children
                // and we need all the properties of the root -> then project * 
                if (foundProjections && expandedProjectionNode.ProjectAllProperties)
                {
                    AppendProjectionOrExpansionPath(projectionPaths, pathSegments, "*");
                } 

                if (projectionPaths.Length > 0) 
                { 
                    if (queryParametersBuilder.Length > 0)
                    { 
                        queryParametersBuilder.Append('&');
                    }

                    queryParametersBuilder.Append("$select=").Append(projectionPaths.ToString()); 
                }
 
                if (expansionPaths.Length > 0) 
                {
                    if (queryParametersBuilder.Length > 0) 
                    {
                        queryParametersBuilder.Append('&');
                    }
 
                    queryParametersBuilder.Append("$expand=").Append(expansionPaths.ToString());
                } 
            } 

            if (queryParametersBuilder.Length > 0) 
            {
                queryParametersBuilder.Append('&');
            }
 
            return queryParametersBuilder;
        } 
 
        /// Pushes a segment from the stack of names being written.
        /// Name of property to push. 
        /// Container to push (possibly null).
        /// Calls to this method should be balanced with calls to PopSegmentName.
        /// true if a segment was push, false otherwise
        private bool PushSegment(string name, ResourceSetWrapper container) 
        {
            if (this.service.Configuration.MaxResultsPerCollection != Int32.MaxValue || 
                (container != null && container.PageSize != 0) || // Complex types have null container , paging should force a push 
                (this.requestDescription.RootProjectionNode != null &&
                 this.requestDescription.RootProjectionNode.ExpansionsSpecified)) 
            {
                if (this.segmentNames == null)
                {
                    this.segmentNames = new List(); 
                    this.segmentContainers = new List();
                    this.segmentResultCounts = new List(); 
                } 

                Debug.Assert( 
                    this.segmentContainers.Count == this.segmentNames.Count,
                    "this.segmentContainers.Count == this.segmentNames.Count -- should always be one-to-one");
                Debug.Assert(
                    this.segmentContainers.Count == this.segmentResultCounts.Count, 
                    "this.segmentContainers.Count == this.segmentResultCounts.Count -- should always be one-to-one");
                this.segmentNames.Add(name); 
                this.segmentContainers.Add(container); 
                this.segmentResultCounts.Add(0);
                Debug.Assert( 
                    this.segmentContainers.Count == this.segmentNames.Count,
                    "this.segmentContainers.Count == this.segmentNames.Count -- should always be one-to-one");
                Debug.Assert(
                    this.segmentContainers.Count == this.segmentResultCounts.Count, 
                    "this.segmentContainers.Count == this.segmentResultCounts.Count -- should always be one-to-one");
                return true; 
            } 

            return false; 
        }

        /// 
        /// Obtains the $top query parameter value. 
        /// 
        /// Integer value for $top or null otherwise. 
        private int? GetTopQueryParameter() 
        {
            String topQueryItem = this.service.OperationContext.Host.GetQueryStringItem(XmlConstants.HttpQueryStringTop); 
            if (!String.IsNullOrEmpty(topQueryItem))
            {
                return Int32.Parse(topQueryItem, System.Globalization.CultureInfo.InvariantCulture);
            } 
            else
            { 
                return null; 
            }
        } 

        /// 
        /// Builds the $skiptoken=[value,value] representation for appending to the next page link URI.
        ///  
        private abstract class SkipTokenBuilder
        { 
            /// Skip token string representation. 
            private StringBuilder skipToken;
 
            /// Constructor.
            public SkipTokenBuilder()
            {
                this.skipToken = new StringBuilder(); 
                this.skipToken.Append(XmlConstants.HttpQueryStringSkipToken).Append('=');
            } 
 
            /// Returns the string representation for $skiptoken query parameter.
            /// String representation for $skiptoken query parameter. 
            public StringBuilder GetSkipToken()
            {
                object[] skipTokenProperties = this.GetSkipTokenProperties();
 
                bool first = true;
                for (int i = 0; i < skipTokenProperties.Length; i++) 
                { 
                    object value = skipTokenProperties[i];
                    string stringValue; 

                    if (value == null)
                    {
                        stringValue = Parsing.ExpressionConstants.KeywordNull; 
                    }
                    else 
                    if (!System.Data.Services.Parsing.WebConvert.TryKeyPrimitiveToString(value, out stringValue)) 
                    {
                        throw new InvalidOperationException(Strings.Serializer_CannotConvertValue(value)); 
                    }

                    if (!first)
                    { 
                        this.skipToken.Append(',');
                    } 
 
                    this.skipToken.Append(System.Uri.EscapeDataString(stringValue));
                    first = false; 
                }

                return this.skipToken;
            } 

            /// Derived classes override this to provide the collection of values for skip token. 
            /// Array of primitive values that comprise the skip token. 
            protected abstract object[] GetSkipTokenProperties();
        } 

        /// Obtains the skip token from IExpandedResult values.
        private class SkipTokenBuilderFromExpandedResult : SkipTokenBuilder
        { 
            /// IExpandedResult to lookup for skip token values.
            private IExpandedResult skipTokenExpandedResult; 
 
            /// Number of values in skip token.
            private int skipTokenExpressionCount; 

            /// Constructor.
            /// IExpandedResult to lookup for skip token values.
            /// Number of values in skip token. 
            public SkipTokenBuilderFromExpandedResult(IExpandedResult skipTokenExpandedResult, int skipTokenExpressionCount)
                : base() 
            { 
                this.skipTokenExpandedResult = skipTokenExpandedResult;
                this.skipTokenExpressionCount = skipTokenExpressionCount; 
            }

            /// Obtains skip token values by looking up IExpandedResult.
            /// Array of primitive values that comprise the skip token. 
            protected override object[] GetSkipTokenProperties()
            { 
                object[] values = new object[this.skipTokenExpressionCount]; 

                for (int i = 0; i < this.skipTokenExpressionCount; i++) 
                {
                    String keyName = XmlConstants.SkipTokenPropertyPrefix + i.ToString(System.Globalization.CultureInfo.InvariantCulture);
                    object value = this.skipTokenExpandedResult.GetExpandedPropertyValue(keyName);
                    if (value == DBNull.Value) 
                    {
                        value = null; 
                    } 

                    values[i] = value; 
                }

                return values;
            } 
        }
 
        /// Obtains the skip token by reading properties directly from an object. 
        private class SkipTokenBuilderFromProperties : SkipTokenBuilder
        { 
            /// Object to read skip token values from.
            private object element;

            /// Collection of properties that comprise the skip token. 
            private ICollection properties;
 
            /// Current provider. 
            private DataServiceProviderWrapper provider;
 
            /// Constructor.
            /// Object to read skip token values from.
            /// Current provider.
            /// Collection of properties that comprise the skip token. 
            public SkipTokenBuilderFromProperties(object element, DataServiceProviderWrapper provider, ICollection properties)
                : base() 
            { 
                this.element = element;
                this.provider = provider; 
                this.properties = properties;
            }

            /// Obtains skip token values by reading properties directly from the last object. 
            /// Array of primitive values that comprise the skip token.
            protected override object[] GetSkipTokenProperties() 
            { 
                object[] values = new object[this.properties.Count];
 
                int propertyIndex = 0;
                foreach (ResourceProperty property in this.properties)
                {
                    object value = WebUtil.GetPropertyValue(this.provider, this.element, null, property, null); 
                    if (value == DBNull.Value)
                    { 
                        value = null; 
                    }
 
                    values[propertyIndex++] = value;
                }

                return values; 
            }
        } 
 
        /// Provides the skip token obtained from the custom paging provider.
        private class SkipTokenBuilderFromCustomPaging : SkipTokenBuilder 
        {
            /// Skip token obtained from custom paging provider.
            private object[] lastTokenValue;
 
            /// Constructor.
            /// Skip token obtained from custom paging provider. 
            public SkipTokenBuilderFromCustomPaging(object[] lastTokenValue) 
                : base()
            { 
                this.lastTokenValue = lastTokenValue;
            }

            /// Provides the skip token values that were obtained from custom paging provider. 
            /// Array of primitive values that comprise the skip token.
            protected override object[] GetSkipTokenProperties() 
            { 
                return this.lastTokenValue;
            } 
        }
    }
}

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
                        

                        

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