动态创建的lambda表达式LINQ + + OrderByDescending [英] dynamically create lambdas expressions + linq + OrderByDescending

问题描述

我怎么可以创建一个动态的lambda表达式通过在LINQ里面我排序依据功能使用？

how can I create a dynamic lambda expression to pass to use in my orderby function inside linq?

我基本上要转变 queryResults.OrderByDescending （）; 在 queryResults.OrderByDescending（myCustomGeneratedLambdaExp）; ，其中 myCustomGeneratedLambdaExp 应是一个字符串containning X => x.name 。

I basically want transform queryResults.OrderByDescending(); in queryResults.OrderByDescending(myCustomGeneratedLambdaExp); where myCustomGeneratedLambdaExp shall be a string containning x => x.name.

感谢

推荐答案

我不知道在哪里你究竟需要动态lambda表达式。不管怎么说，动态生成lambda表达式的最好方法是使用表达式树。以下是关于这个问题的两个很好的教程：

I'm not sure where exactly did you need dynamic lambda expressions. Anyways, the best way to generate lambda expressions dynamically is by using expression trees. Here are two good tutorials on the subject:

• 的 http://www.davidhayden.com/blog/dave/archive/2006/12/18/ExpressionTrees.aspx

的 http://marlongrech.wordpress.com/2008/01/08/working-with-expression-trees-part-1/

这代码生成一个lambda表达式就像你问一个（X => x.name）：

This code generates a lambda expression like the one you asked for ("x => x.name"):

MemberInfo member = typeof(AClassWithANameProperty).GetProperty("Name");

//Create 'x' parameter expression
ParameterExpression xParameter = Expression.Parameter(typeof(object), "x");

//Create body expression
Expression body = Expression.MakeMemberAccess(targetParameter, member);

//Create and compile lambda
var lambda = Expression.Lambda<LateBoundGetMemberValue>(
    Expression.Convert(body, typeof(string)),
    targetParameter
);
return lambda.Compile();

希望这有助于

hope this helps

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