Sql8ExpressionRewriter.cs source code in C# .NET

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Code:

/ 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / DataEntity / System / Data / SqlClient / SqlGen / Sql8ExpressionRewriter.cs / 1305376 / Sql8ExpressionRewriter.cs

                            //---------------------------------------------------------------------- 
// 
//      Copyright (c) Microsoft Corporation.  All rights reserved.
// 
// 
// @owner  [....]
// @backupOwner [....] 
//--------------------------------------------------------------------- 

using System; 
using System.Collections.Generic;
using System.Diagnostics;
using System.Globalization;
 
using System.Data.Common;
using System.Data.Common.CommandTrees; 
using System.Data.Common.CommandTrees.Internal; 

using System.Data.Metadata.Edm; 
using System.Data.Common.CommandTrees.ExpressionBuilder;

namespace System.Data.SqlClient.SqlGen
{ 
    /// 
    /// Rewrites an expression tree to make it suitable for translation to SQL appropriate for SQL Server 2000 
    /// In particular, it replaces expressions that are not directly supported on SQL Server 2000 
    /// with alternative translations. The following expressions are translated:
    ///  
    /// 
    /// 
    /// 
    ///  
    ///
    /// The other expressions are copied unmodified. 
    /// The new expression belongs to a new query command tree. 
    /// 
    internal class Sql8ExpressionRewriter : DbExpressionRebinder 
    {
        #region Entry Point
        /// 
        /// The only entry point. 
        /// Rewrites the given tree by replacing expressions that are not directly supported on SQL Server 2000
        /// with alterntive translations. 
        ///  
        /// The tree to rewrite
        /// The new tree 
        internal static DbQueryCommandTree Rewrite(DbQueryCommandTree originalTree)
        {
            Debug.Assert(originalTree != null, "OriginalTree is null");
            Sql8ExpressionRewriter rewriter = new Sql8ExpressionRewriter(originalTree.MetadataWorkspace); 
            DbExpression newQuery = rewriter.VisitExpression(originalTree.Query);
            return DbQueryCommandTree.FromValidExpression(originalTree.MetadataWorkspace, originalTree.DataSpace, newQuery); 
        } 
        #endregion
 
        #region Constructor
        /// 
        /// Private Constructor.
        ///  
        /// 
        private Sql8ExpressionRewriter(MetadataWorkspace metadata) 
            :base(metadata) 
        {
        } 
        #endregion

        #region DbExpressionVisitor Members
        ///  
        /// 
        ///  
        ///  
        /// 
        public override DbExpression Visit(DbExceptExpression e) 
        {
            return TransformIntersectOrExcept(VisitExpression(e.Left), VisitExpression(e.Right), DbExpressionKind.Except);
        }
 
        /// 
        ///  
        ///  
        /// 
        ///  
        public override DbExpression Visit(DbIntersectExpression e)
        {
            return TransformIntersectOrExcept(VisitExpression(e.Left), VisitExpression(e.Right), DbExpressionKind.Intersect);
        } 

        ///  
        /// Logicaly,  translates to: 
        /// SELECT Y.x1, Y.x2, ..., Y.xn
        /// FROM ( 
        ///     SELECT X.x1, X.x2, ..., X.xn,
        ///     FROM input AS X
        ///        EXCEPT
        ///     SELECT TOP(count) Z.x1, Z.x2, ..., Z.xn 
        ///     FROM input AS Z
        ///     ORDER BY sk1, sk2, ... 
        ///     ) AS Y 
        /// ORDER BY sk1, sk2, ...
        /// 
        /// Here, input refers to the input of the , and count to the count property of the .
        /// The implementation of EXCEPT is non-duplicate eliminating, and does equality comparison only over the
        /// equality comparable columns of the input.
        /// 
        /// This corresponds to the following expression tree:
        /// 
        /// SORT 
        ///  |
        /// NON-DISTINCT EXCEPT  (specially translated,  
        ///  |
        ///  | - Left:  clone of input
        ///  | - Right:
        ///       | 
        ///      Limit
        ///       | 
        ///       | - Limit: Count 
        ///       | - Input
        ///             | 
        ///            Sort
        ///             |
        ///            input
        /// 
        /// 
        ///  
        ///  
        public override DbExpression Visit(DbSkipExpression e)
        { 
            //Build the right input of the except
            DbExpression rightInput = VisitExpressionBinding(e.Input).Sort(VisitSortOrder(e.SortOrder)).Limit(VisitExpression(e.Count));

            //Build the left input for the except 
            DbExpression leftInput = VisitExpression(e.Input.Expression); //Another copy of the input
 
            IList sortOrder = VisitSortOrder(e.SortOrder); //Another copy of the sort order 

            // Create a list of the sort expressions to be used for translating except 
            IList sortExpressions = new List(e.SortOrder.Count);
            foreach (DbSortClause sortClause in sortOrder)
            {
                //We only care about property expressions, not about constants 
                if (sortClause.Expression.ExpressionKind == DbExpressionKind.Property)
                { 
                    sortExpressions.Add((DbPropertyExpression)sortClause.Expression); 
                }
            } 

            DbExpression exceptExpression = TransformIntersectOrExcept(leftInput, rightInput, DbExpressionKind.Skip, sortExpressions, e.Input.VariableName);

            DbExpression result = exceptExpression.BindAs(e.Input.VariableName).Sort(sortOrder); 

            return result; 
        } 
        #endregion
 
        #region DbExpressionVisitor Member Helpers

        /// 
        /// This method is invoked when tranforming  and  by doing comparison over all input columns. 
        /// 
        ///  
        ///  
        /// 
        ///  
        /// 
        private DbExpression TransformIntersectOrExcept(DbExpression left, DbExpression right, DbExpressionKind expressionKind)
        {
            return TransformIntersectOrExcept( left,  right,  expressionKind, null, null); 
        }
 
        ///  
        /// This method is used for translating  and ,
        /// and for translating the "Except" part of . 
        /// into the follwoing expression:
        ///
        /// A INTERSECT B, A EXCEPT B
        /// 
        /// (DISTINCT)
        ///  | 
        /// FILTER 
        ///  |
        ///  | - Input: A 
        ///  | - Predicate:(NOT)
        ///                 |
        ///                 ANY
        ///                 | 
        ///                 | - Input: B
        ///                 | - Predicate:  (B.b1 = A.a1 or (B.b1 is null and A.a1 is null)) 
        ///                             AND (B.b2 = A.a2 or (B.b2 is null and A.a2 is null)) 
        ///                             AND ...
        ///                             AND (B.bn = A.an or (B.bn is null and A.an is null))) 
        ///
        /// Here, A corresponds to right and B to left.
        /// (NOT) is present when transforming Except
        /// for the purpose of translating  or . 
        /// (DISTINCT) is present when transforming for the purpose of translating
        ///  or . 
        /// 
        /// For , the input to ANY is caped with project which projects out only
        /// the columns represented in the sortExpressionsOverLeft list and only these are used in the predicate. 
        /// This is because we want to support skip over input with non-equal comarable columns and we have no way to recognize these.
        /// 
        /// 
        ///  
        /// 
        /// note that this list gets destroyed by this method 
        ///  
        /// 
        private DbExpression TransformIntersectOrExcept(DbExpression left, DbExpression right, DbExpressionKind expressionKind, IList sortExpressionsOverLeft, string sortExpressionsBindingVariableName) 
        {
            bool negate = (expressionKind == DbExpressionKind.Except) || (expressionKind == DbExpressionKind.Skip);
            bool distinct = (expressionKind == DbExpressionKind.Except) || (expressionKind == DbExpressionKind.Intersect);
 
            DbExpressionBinding leftInputBinding = left.Bind();
            DbExpressionBinding rightInputBinding = right.Bind(); 
 
            IList leftFlattenedProperties = new List();
            IList rightFlattenedProperties = new List(); 

            FlattenProperties(leftInputBinding.Variable, leftFlattenedProperties);
            FlattenProperties(rightInputBinding.Variable, rightFlattenedProperties);
 
            //For Skip, we need to ignore any columns that are not in the original sort list. We can recognize these by comparing the left flattened properties and
            // the properties in the list sortExpressionsOverLeft 
            // If any such columns exist, we need to add an additional project, to keep the rest of the columns from being projected, as if any among these 
            // are non equal comparable, SQL Server 2000 throws.
            if (expressionKind == DbExpressionKind.Skip) 
            {
                if (RemoveNonSortProperties(leftFlattenedProperties, rightFlattenedProperties, sortExpressionsOverLeft, leftInputBinding.VariableName, sortExpressionsBindingVariableName))
                {
                   rightInputBinding = CapWithProject(rightInputBinding, rightFlattenedProperties); 
                }
            } 
 
            Debug.Assert(leftFlattenedProperties.Count == rightFlattenedProperties.Count, "The left and the right input to INTERSECT or EXCEPT have a different number of properties");
            Debug.Assert(leftFlattenedProperties.Count != 0, "The inputs to INTERSECT or EXCEPT have no properties"); 

            //Build the predicate for the quantifier:
            //   (B.b1 = A.a1 or (B.b1 is null and A.a1 is null))
            //      AND (B.b2 = A.a2 or (B.b2 is null and A.a2 is null)) 
            //      AND ...
            //      AND (B.bn = A.an or (B.bn is null and A.an is null))) 
            DbExpression existsPredicate = null; 

            for (int i = 0; i < leftFlattenedProperties.Count; i++) 
            {
                //A.ai == B.bi
                DbExpression equalsExpression = leftFlattenedProperties[i].Equal(rightFlattenedProperties[i]);
 
                //A.ai is null AND B.bi is null
                DbExpression leftIsNullExpression = leftFlattenedProperties[i].IsNull(); 
                DbExpression rightIsNullExpression = rightFlattenedProperties[i].IsNull(); 
                DbExpression bothNullExpression = leftIsNullExpression.And(rightIsNullExpression);
 
                DbExpression orExpression = equalsExpression.Or(bothNullExpression);

                if (i == 0)
                { 
                    existsPredicate = orExpression;
                } 
                else 
                {
                    existsPredicate = existsPredicate.And(orExpression); 
                }
            }

            //Build the quantifier 
            DbExpression quantifierExpression = rightInputBinding.Any(existsPredicate);
 
            DbExpression filterPredicate; 

            //Negate if needed 
            if (negate)
            {
                filterPredicate = quantifierExpression.Not();
            } 
            else
            { 
                filterPredicate = quantifierExpression; 
            }
 
            //Build the filter
            DbExpression result = leftInputBinding.Filter(filterPredicate);

            //Apply distinct in needed 
            if (distinct)
            { 
                result = result.Distinct(); 
            }
 
            return result;
        }

        ///  
        /// Adds the flattened properties on the input to the flattenedProperties list.
        ///  
        ///  
        /// 
        private void FlattenProperties(DbExpression input, IList flattenedProperties) 
        {
            IList properties = TypeHelpers.GetProperties(input.ResultType);
            Debug.Assert(properties.Count != 0, "No nested properties when FlattenProperties called?");
 
            for (int i = 0; i < properties.Count; i++)
            { 
                DbExpression propertyInput = input; 

                DbPropertyExpression propertyExpression = propertyInput.Property(properties[i]); 
                if (TypeSemantics.IsPrimitiveType(properties[i].TypeUsage))
                {
                    flattenedProperties.Add(propertyExpression);
                } 
                else
                { 
                    Debug.Assert(TypeSemantics.IsEntityType(properties[i].TypeUsage) || TypeSemantics.IsRowType(properties[i].TypeUsage), 
                        "The input to FlattenProperties is not of EntityType or RowType?");
 
                    FlattenProperties(propertyExpression, flattenedProperties);
                }
            }
        } 

 
        ///  
        /// Helper method for 
        /// Removes all pairs of property expressions from list1 and list2, for which the property expression in list1 
        /// does not have a 'matching' property expression in list2.
        /// The lists list1 and list2 are known to not create duplicate, and the purpose of the sortList is just for this method.
        /// Thus, to optimize the match process, we remove the seen property expressions from the sort list in 
        /// when iterating both list simultaneously. 
        /// 
        ///  
        ///  
        /// 
        ///  
        /// 
        /// 
        private static bool RemoveNonSortProperties(IList list1, IList list2, IList sortList, string list1BindingVariableName, string sortExpressionsBindingVariableName)
        { 
            bool result = false;
            for (int i = list1.Count - 1; i >= 0; i--) 
            { 
                if (!HasMatchInList(list1[i], sortList, list1BindingVariableName, sortExpressionsBindingVariableName))
                { 
                    list1.RemoveAt(i);
                    list2.RemoveAt(i);
                    result = true;
                } 
            }
            return result; 
        } 

        ///  
        /// Helper method for 
        /// Checks whether expr has a 'match' in the given list of property expressions.
        /// If it does, the matching expression is removed form the list, to speed up future matching.
        ///  
        /// 
        ///  
        ///  
        /// 
        ///  
        private static bool HasMatchInList(DbPropertyExpression expr, IList list, string exprBindingVariableName, string listExpressionsBindingVariableName)
        {
            for (int i=0; i 
        /// Determines whether two expressions match.
        /// They match if they are  of the shape 
        ///   expr1 -> DbPropertyExpression(... (DbPropertyExpression(DbVariableReferenceExpression(expr1BindingVariableName), nameX), ..., name1)
        ///   expr1 -> DbPropertyExpression(... (DbPropertyExpression(DbVariableReferenceExpression(expr2BindingVariableName), nameX), ..., name1),
        ///
        /// i.e. if they only differ in the name of the binding. 
        /// 
        ///  
        ///  
        /// 
        ///  
        /// 
        private static bool AreMatching(DbPropertyExpression expr1, DbPropertyExpression expr2, string expr1BindingVariableName, string expr2BindingVariableName)
        {
            if (expr1.Property.Name != expr2.Property.Name) 
            {
                return false; 
            } 

            if (expr1.Instance.ExpressionKind != expr2.Instance.ExpressionKind) 
            {
                return false;
            }
 
            if (expr1.Instance.ExpressionKind == DbExpressionKind.Property)
            { 
                return AreMatching((DbPropertyExpression)expr1.Instance, (DbPropertyExpression)expr2.Instance, expr1BindingVariableName, expr2BindingVariableName); 
            }
 
            DbVariableReferenceExpression instance1 =  (DbVariableReferenceExpression)expr1.Instance;
            DbVariableReferenceExpression instance2 =  (DbVariableReferenceExpression)expr2.Instance;

            return (String.Equals(instance1.VariableName, expr1BindingVariableName, StringComparison.Ordinal) 
                && String.Equals(instance2.VariableName, expr2BindingVariableName, StringComparison.Ordinal));
        } 
 
        /// 
        /// Helper method for  
        /// Creates a  over the given inputBinding that projects out the given flattenedProperties.
        /// and updates the flattenedProperties to be over the newly created project.
        /// 
        ///  
        /// 
        /// An  over the newly created  
        private DbExpressionBinding CapWithProject(DbExpressionBinding inputBinding, IList flattenedProperties) 
        {
            List> projectColumns = new List>(flattenedProperties.Count); 

            //List of all the columnNames used in the projection.
            Dictionary columnNames = new Dictionary(flattenedProperties.Count);
 
            foreach (DbPropertyExpression pe in flattenedProperties)
            { 
                //There may be conflicting property names, thus we may need to rename. 
                string name = pe.Property.Name;
                int i; 
                if (columnNames.TryGetValue(name, out i))
                {
                    string newName;
                    do 
                    {
                        ++i; 
                        newName = name + i.ToString(System.Globalization.CultureInfo.InvariantCulture); 
                    } while (columnNames.ContainsKey(newName));
 
                    columnNames[name] = i;
                    name = newName;
                }
 
                // Add this column name to list of known names so that there are no subsequent
                // collisions 
                columnNames[name] = 0; 
                projectColumns.Add(new KeyValuePair(name, pe));
            } 

            //Build the project
            DbExpression rowExpr = DbExpressionBuilder.NewRow(projectColumns);
            DbProjectExpression projectExpression = inputBinding.Project(rowExpr); 

            //Create the new inputBinding 
            DbExpressionBinding resultBinding = projectExpression.Bind(); 

            //Create the list of flattenedProperties over the new project 
            flattenedProperties.Clear();
            RowType rowExprType = (RowType)rowExpr.ResultType.EdmType;

            foreach (KeyValuePair column in projectColumns) 
            {
                EdmProperty prop = rowExprType.Properties[column.Key]; 
                flattenedProperties.Add(resultBinding.Variable.Property(prop)); 
            }
            return resultBinding; 
        }

        #endregion
    } 
}

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

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