关于LinQ的动态查询

Question

支持楼主，只是有地方不懂  这个函数的返回值是什么 类型啊 Expression <Func <TEntity, bool>> 
我也要做个linq 的动态查询，其它的地方都懂了，可能是我范型不太会,请指点啊

Answer 1

用linq做动态查询,还不如直接拼字符串直观.
本来很简单的问题搞复杂了.
codeporject上有个开源的项目,用来做动态查询是非常不错的.楼主可找找.

Answer 2

        NorthwindDataContext northwind = new NorthwindDataContext();        var query = northwind.Products
                             .Where("CategoryID = 3 AND UnitPrice > 3")
                             .OrderBy("SupplierID");        GridView1.DataSource = query;
        GridView1.DataBind();部分代码        // =, ==, !=, <>, >, >=, <, <= operators
        Expression ParseComparison()
        {
            Expression left = ParseAdditive();
            while (token.id == TokenId.Equal || token.id == TokenId.DoubleEqual ||
                token.id == TokenId.ExclamationEqual || token.id == TokenId.LessGreater ||
                token.id == TokenId.GreaterThan || token.id == TokenId.GreaterThanEqual ||
                token.id == TokenId.LessThan || token.id == TokenId.LessThanEqual)
            {
                Token op = token;
                NextToken();
                Expression right = ParseAdditive();
                bool isEquality = op.id == TokenId.Equal || op.id == TokenId.DoubleEqual ||
                    op.id == TokenId.ExclamationEqual || op.id == TokenId.LessGreater;
                if (isEquality && !left.Type.IsValueType && !right.Type.IsValueType)
                {
                    if (left.Type != right.Type)
                    {
                        if (left.Type.IsAssignableFrom(right.Type))
                        {
                            right = Expression.Convert(right, left.Type);
                        }
                        else if (right.Type.IsAssignableFrom(left.Type))
                        {
                            left = Expression.Convert(left, right.Type);
                        }
                        else
                        {
                            throw IncompatibleOperandsError(op.text, left, right, op.pos);
                        }
                    }
                }
                else if (IsEnumType(left.Type) || IsEnumType(right.Type))
                {
                    if (left.Type != right.Type)
                    {
                        Expression e;
                        if ((e = PromoteExpression(right, left.Type, true)) != null)
                        {
                            right = e;
                        }
                        else if ((e = PromoteExpression(left, right.Type, true)) != null)
                        {
                            left = e;
                        }
                        else
                        {
                            throw IncompatibleOperandsError(op.text, left, right, op.pos);
                        }
                    }
                }
                else
                {
                    CheckAndPromoteOperands(isEquality ? typeof(IEqualitySignatures) : typeof(IRelationalSignatures),
                        op.text, ref left, ref right, op.pos);
                }
                switch (op.id)
                {
                    case TokenId.Equal:
                    case TokenId.DoubleEqual:
                        left = GenerateEqual(left, right);
                        break;
                    case TokenId.ExclamationEqual:
                    case TokenId.LessGreater:
                        left = GenerateNotEqual(left, right);
                        break;
                    case TokenId.GreaterThan:
                        left = GenerateGreaterThan(left, right);
                        break;
                    case TokenId.GreaterThanEqual:
                        left = GenerateGreaterThanEqual(left, right);
                        break;
                    case TokenId.LessThan:
                        left = GenerateLessThan(left, right);
                        break;
                    case TokenId.LessThanEqual:
                        left = GenerateLessThanEqual(left, right);
                        break;
                }
            }
            return left;
        }
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http://download.csdn.net/source/1726289