C# DbSkipExpression类代码示例

        public override Expression Visit(DbSkipExpression expression)
        {
            Expression source = this.Visit(expression.Input.Expression);
            Type sourceType = TypeHelper.GetElementType(source.Type);

            // Skip cannot be used without sorting
            Expression result = this.CreateOrderByExpression(expression.SortOrder, expression.Input.VariableName, source);

            return queryMethodExpressionBuilder.Skip(result, this.Visit(expression.Count, typeof(int)));
        }

        /// <summary>
        /// Implements the visitor pattern for <see cref="T:System.Data.Common.CommandTrees.DbSkipExpression"/>.
        /// </summary>
        /// <param name="expression">The <see cref="T:System.Data.Common.CommandTrees.DbSkipExpression"/> that is visited.</param>
        public override void Visit(DbSkipExpression expression)
        {
            if (expression == null)
            {
                throw new ArgumentNullException("expression");
            }

            expression.Count.Accept(this);
            expression.Input.Expression.Accept(this);
            foreach (var sortClause in expression.SortOrder)
            {
                sortClause.Expression.Accept(this);
            }
        }

 internal SkipLifter(DbSkipExpression skip, AliasGenerator aliasGenerator)
     : base(skip, aliasGenerator)
 {
     _skip = skip;
     _source = skip.Input.Expression;
 }

 internal ProjectSkipLifter(DbProjectExpression project, DbSkipExpression skip, AliasGenerator aliasGenerator)
     : base(project, aliasGenerator)
 {
     _project = project;
     _skip = skip;
     _source = _skip.Input.Expression;
 }

 internal LimitSkipLifter(DbLimitExpression limit, DbSkipExpression skip, AliasGenerator aliasGenerator)
     : base(limit, aliasGenerator)
 {
     _limit = limit;
     _skip = skip;
     _source = skip.Input.Expression;
 }

            public override DbExpression Visit(DbSkipExpression expression)
            {
                Check.NotNull(expression, "expression");

                var found = Find(expression.Input.Expression);
                if (!ReferenceEquals(found, expression.Input.Expression))
                {
                    return found.BindAs(expression.Input.VariableName).Skip(expression.SortOrder, expression.Count);
                }
                else
                {
                    return expression;
                }
            }

        public override SqlFragment Visit(DbSkipExpression expression)
        {
            SelectStatement select = VisitInputExpressionEnsureSelect(expression.Input.Expression, expression.Input.VariableName,
                expression.Input.VariableType);

            foreach (DbSortClause sortClause in expression.SortOrder)
            {
                select.AddOrderBy(
                    new SortFragment(sortClause.Expression.Accept(this), sortClause.Ascending));
            }


            select = WrapIfNotCompatible(select, expression.ExpressionKind);
            select.Skip = expression.Count.Accept(this);
            return select;
        }

        /// <summary>
        /// Logicaly, <see cref="DbSkipExpression"/> 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 <see cref="DbSkipExpression"/>, and count to the count property of the <see cref="DbSkipExpression"/>.
        /// 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, <see cref="TransformIntersectOrExcept(DbExpression left, DbExpression right, DbExpressionKind expressionKind, IList<DbPropertyExpression> sortExpressionsOverLeft, string sortExpressionsBindingVariableName)"/>
        ///  |
        ///  | - Left:  clone of input
        ///  | - Right:
        ///       |
        ///      Limit
        ///       |
        ///       | - Limit: Count
        ///       | - Input
        ///             |
        ///            Sort
        ///             |
        ///            input
        ///    
        /// </summary>
        /// <param name="e"></param>
        /// <returns></returns>
        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
            var leftInput = VisitExpression(e.Input.Expression); //Another copy of the input

            var sortOrder = VisitSortOrder(e.SortOrder); //Another copy of the sort order

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

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

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

            return result;
        }

		public override void Visit(DbSkipExpression expression)
		{
			throw new NotSupportedException("Visit(\"SkipExpression\") is not supported.");
		}

 /// <summary>
 ///     Visitor pattern method for DbSkipExpression.
 /// </summary>
 /// <param name="expression"> The DbSkipExpression that is being visited. </param>
 public abstract void Visit(DbSkipExpression expression);

        /// <summary>
        /// Visitor pattern method for <see cref="DbSkipExpression"/>.
        /// </summary>
        /// <param name="expression">The DbSkipExpression that is being visited.</param>
        /// <exception cref="ArgumentNullException"><paramref name="expression"/> is null</exception>
        public override void Visit(DbSkipExpression expression)
        {
            // #433613: PreSharp warning 56506: Parameter 'expression' to this public method must be validated: A null-dereference can occur here.
            EntityUtil.CheckArgumentNull(expression, "expression");

            VisitExpressionBindingPre(expression.Input);
            foreach (DbSortClause sortKey in expression.SortOrder)
            {
                VisitExpression(sortKey.Expression);
            }
            VisitExpressionBindingPost(expression.Input);
            VisitExpression(expression.Count);
        }

 public override void Visit(DbSkipExpression e)
 {
     Begin(e);
     Dump(e.Input, "Input");
     Dump(e.SortOrder);
     Dump(e.Count, "Count");
     End(e);
 }

 public override void Visit(DbSkipExpression expression) { }

        public override void Visit(DbSkipExpression e)
        {
            Check.NotNull(e, "e");

            Begin(e);
            Dump(e.Input, "Input");
            Dump(e.SortOrder);
            Dump(e.Count, "Count");
            End(e);
        }

 public override DbExpression Visit(DbSkipExpression expression)
 {
     DbExpression found = Find(expression.Input.Expression);
     if (!object.ReferenceEquals(found, expression.Input.Expression))
     {
         return found.BindAs(expression.Input.VariableName).Skip(expression.SortOrder, expression.Count);
     }
     else
     {
         return expression;
     }
 }