创建用于访问泛型类型的属性的表达式树 [英] Creating expression tree for accessing a Generic type's property

问题描述

我需要编写一个通用方法，该方法以字符串格式获取通用类型的实例和属性名称，并返回一个表达式树

I need to write a generic method which takes the instance of the generic type and the property name in string format and return an Expression tree

我需要转换一个简单的lambda表达式

I need to convert a simple lambda expression

a => a.SomePropertyName

其中a是通用类型，其将具有名称为SomePropertyName

我知道我们可以使用以下反射代码来获取属性信息

I know that we can get the property information using the following reflection code

System.Reflection.PropertyInfo propInfo = a.GetType().GetProperty("SomePropertyName");

这可能很简单，但是我对表达式树不熟悉，如果有类似的问题，请链接它并关闭它

This might be very simple, but I'm not well versed with Expression trees, If there is a similar question, please link it and close this

推荐答案

假设事先不知道参数类型和返回类型，则可能必须使用一些object，但从根本上讲，这仅仅是:

Assuming the parameter type and return type aren't known in advance, you may have to use some object, but fundamentally this is just:

var p = Expression.Parameter(typeof(object));
var expr = Expression.Lambda<Func<object, object>>(
    Expression.Convert(
        Expression.PropertyOrField(
             Expression.Convert(p, a.GetType()), propName), typeof(object)), p);

如果输入和输出类型已知，则可以调整Func<,>参数，也可以删除Expression.Convert.在极端情况下，您可以通过以下方式获得lambda ，而无需知道lambda的签名:

If the input and output types are known, you can tweak the Func<,> parameters, and maybe remove the Expression.Convert. At the extreme end you can get a lambda without knowing the signature of lambda, via:

var p = Expression.Parameter(a.GetType());
var expr = Expression.Lambda(Expression.PropertyOrField(p, propName), p);

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