C#表达式转换方便使用==还是equals运营商和外部参数 [英] C# Expressions easy conversion with == or Equals operator and external parameter
问题描述
比方说,我有两个参数:
参数1,需要一个T和从中获取了相关产品的标识表达
表达式来; Func键< T,INT>> prodIdProperty = X => x.Product.Id
参数2的productid与比较,让我们说
INT的productid = 5;
有什么办法,我可以运行时改变这个(代码)进入这样一个新的表达方式:
表达式来; Func键< T,BOOL>> prodIdProperty = X => x.Product.Id == 5
基本上,我需要是这样的:
表达式来; Func键< T,BOOL>> TransformToPredicate(表达式来; Func键< T,INT>> prodIdProperty,诠释产品ID){
//插入表情变换魔术我似乎没有掌握...
}
我需要这个,因为我希望把它作为一个谓语我的EF Where子句,这意味着我不能包括我prodIdProperty的编译版本因为它需要调用的invoke()至极,不支持
(我已经试过的这个问题,但我觉得我过于复杂那儿)
< DIV CLASS =h2_lin>解决方案
这听起来像你想要的东西,如:
表达式来; FUNC< T,BOOL>> TransformToPredicate(
表达式来; Func键< T,INT>> prodIdProperty,
INT的productId)
{
表达等于= Expression.Equal(prodIdProperty.Body,
表达.Constant(productId参数));
返回Expression.Lambda<&Func键LT; T,BOOL>>(等于,prodIdProperty.Parameters);
}
显示在用行动表明示例代码:
使用系统;使用System.Linq.Expressions
;
类测试
{
静态表达式来; Func键< T,BOOL>> TransformToPredicate< T>(
表达式来; Func键< T,INT>> prodIdProperty,
INT的productId)
{
表达等于= Expression.Equal(prodIdProperty.Body,
Expression.Constant(productId参数));
返回Expression.Lambda<&Func键LT; T,BOOL>>(等于,prodIdProperty.Parameters);
}
静态无效的主要()
{
表达式来; Func键<字符串,整数>>长度= X => x.Length;
变种谓词= TransformToPredicate(长度,5);
变种编译= predicate.Compile();
Console.WriteLine(编译(你好)); //真
Console.WriteLine(编译(富)); //假
}
}
Let's say i had two parameters:
parameter 1 an expression that takes a T and fetches the associated product's ID from it
Expression<Func<T,int>> prodIdProperty = x=>x.Product.Id
parameter 2 a productid to compare with , let's say
int productid = 5;
Is there any way I could runtime transform this (in code) into a new expression like this:
Expression<Func<T,bool>> prodIdProperty = x=>x.Product.Id == 5
I basically need something like this:
Expression<Func<T,bool>> TransformToPredicate(Expression<Func<T,int>> prodIdProperty,int productid){
//insert expression transform magic I don't seem to grasp...
}
I need this because I want to pass it as a predicate to my EF Where clause, that means I cannot included Compiled versions of my prodIdProperty as It requires calling Invoke() wich is not supported
(I already tried formulating my problem another way in this question, but I think I overcomplicated it there)
It sounds like you want something like:
Expression<Func<T, bool>> TransformToPredicate(
Expression<Func<T, int>> prodIdProperty,
int productId)
{
Expression equals = Expression.Equal(prodIdProperty.Body,
Expression.Constant(productId));
return Expression.Lambda<Func<T, bool>>(equals, prodIdProperty.Parameters);
}
Sample code showing it in action:
using System;
using System.Linq.Expressions;
class Test
{
static Expression<Func<T, bool>> TransformToPredicate<T>(
Expression<Func<T, int>> prodIdProperty,
int productId)
{
Expression equals = Expression.Equal(prodIdProperty.Body,
Expression.Constant(productId));
return Expression.Lambda<Func<T, bool>>(equals, prodIdProperty.Parameters);
}
static void Main()
{
Expression<Func<string, int>> length = x => x.Length;
var predicate = TransformToPredicate(length, 5);
var compiled = predicate.Compile();
Console.WriteLine(compiled("Hello")); // True
Console.WriteLine(compiled("Foo")); // False
}
}
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