Question

Supating I with the following LambdaExpression:

var itemParam = Expression.Parameter(typeof(Thing), "thing");
var someValue = "ABCXYZ123"; // value to compare

LambdaExpression lex = Expression.Lambda(
  Expression.Equal(
    Expression.Property(itemParam, "Id"), // I want ID to be a Body expression parameter
    Expression.Constant(someValue)
  ), itemParm);

And I want the property name (2nd parameter) in the Expression.Property(...) factory to be a parameter, how do I go about doing this?

我希望看到这样的建筑家,但现在还没有:

Expresssion.Property(Expression instance, Expression propName)

我能否把直截了当的压缩转化为必要的扼杀或成员。 Maybe 我这样说是错误的。

My hunch is that because these expression trees, when compiled, become lightweight IL, that member access information is required, thus, the names of members and properties must be provided when constructing expression trees.

感谢任何ti!

EDIT: Wanted to add that this will be used as an argument to the Enumerable.Where(...) extension method for determining a match on a relationship between two classes / entities.

Answer 1

Expression树是指你在C#/VB中看到的同样类型的IL结构。 NET方案。您不能将这种财产表达与你不能“参数”以下法典的相同理由相混淆:

var x = new MyClass {Id = 1, Name = "hello"}; var propName = "Id"; var xId = x.propName; // <-- This will not compile

If you need to implement this functionality, and your expression trees are not passed to IQueryable<T>, you can write a helper function taking an object and a string, and returning value of that object s property identified by the string; then you can use Expression.Call to invoke that helper function into the expression tree that you are building.

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