C# DbExpression.Bind方法代码示例

        /// <summary>
        /// This method is used for translating <see cref="DbIntersectExpression"/> and <see cref="DbExceptExpression"/>,
        /// and for translating the "Except" part of <see cref="DbSkipExpression"/>.
        /// 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 <see cref="DbExceptExpression"/> or <see cref="DbSkipExpression"/>.   
        /// (DISTINCT) is present when transforming for the purpose of translating 
        /// <see cref="DbExceptExpression"/> or <see cref="DbIntersectExpression"/>.  
        /// 
        /// For <see cref="DbSkipExpression"/>, 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.
        /// </summary>
        /// <param name="left"></param>
        /// <param name="right"></param>
        /// <param name="expressionKind"></param>
        /// <param name="sortExpressionsOverLeft">note that this list gets destroyed by this method</param>
        /// <param name="sortExpressionsBindingVariableName"></param>
        /// <returns></returns>
        private DbExpression TransformIntersectOrExcept(
            DbExpression left, DbExpression right, DbExpressionKind expressionKind, IList<DbPropertyExpression> sortExpressionsOverLeft,
            string sortExpressionsBindingVariableName)
        {
            var negate = (expressionKind == DbExpressionKind.Except) || (expressionKind == DbExpressionKind.Skip);
            var distinct = (expressionKind == DbExpressionKind.Except) || (expressionKind == DbExpressionKind.Intersect);

            var leftInputBinding = left.Bind();
            var rightInputBinding = right.Bind();

            IList<DbPropertyExpression> leftFlattenedProperties = new List<DbPropertyExpression>();
            IList<DbPropertyExpression> rightFlattenedProperties = new List<DbPropertyExpression>();

            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 (var 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);
                }
//.........这里部分代码省略.........