类型成员的表达式导致不同的表达式（MemberExpression，UnaryExpression） [英] Expression for Type members results in different Expressions (MemberExpression, UnaryExpression)

问题描述

我有一个表达式指向我的类型的属性。
但它不适用于每个属性类型。 不意味着意味着
它导致不同的表达式类型。我以为会导致
MemberExpression ，但情况并非如此。

I have a expression to point on a property of my type. But it does not work for every property type. "Does not mean" means it result in different expression types. I thought it will ever result in a MemberExpression but this is not the case.

code> int 和 Guid 它会导致 UnaryExpression 和 string
在 MemberExpression 。

For int and Guid it results in a UnaryExpression and for string in a MemberExpression.

我是有点困惑;）

我的课程

public class Person
{
    public string Name { get; set; }
    public int Age { get; set; }
}

测试代码

Person p = new Person { Age = 16, Name = "John" };

Expression<Func<Person, object>> expression1 = x => x.Age;
// expression1.Body = UnaryExpression;

Expression<Func<Person, object>> expression2 = x => x.Name;
// expression2.Body = MemberExpression;

问题

表达式并检查它们是否是平均值
相同的类型和相同的属性？

Question

How can i compare two expressions and check if they are mean the same type and same property ?

感谢使用者带给我的用户 dasblinkenlight 在正确的轨道上。

Thanks to user dasblinkenlight who brought me on the right track.

他提供了方法

private static MemberExpression GetMemberExpression<T>(
    Expression<Func<T,object>> exp
) {
    var member = expr.Body as MemberExpression;
    var unary = expr.Body as UnaryExpression;
    return member ?? (unary != null ? unary.Operand as MemberExpression : null);
}

我写了以下扩展方法来比较 GetMemberExpression
方法，并检查 GetMemberExpression（）。Member.Name 是否相同。

I wrote the following extension method to compare the results of the GetMemberExpression methods and check if GetMemberExpression().Member.Name are the same.

private static bool IsSameMember<T>(this Expression<Func<T, object>> expr1, Expression<Func<T, object>> expr2)
{
    var result1 = GetMemberExpression(expr1);
    var result2 = GetMemberExpression(expr2);

    if (result1 == null || result2 == null)
       return false;

    return result1.Member.Name == result2.Member.Name;
}

推荐答案

年龄是一种值类型。为了强制将一个值类型转换为 Func< Person，object> ，编译器需要插入一个Convert(expr，typeof（object）） ，a UnaryExpression 。

The reason this happens is that Age is a value type. In order to coerce an expression returning a value type into Func<Person,object> the compiler needs to insert a Convert(expr, typeof(object)), a UnaryExpression.

对于 string s和其他引用类型，然而，不需要框，因此返回直成员表达式。

For strings and other reference types, however, there is no need to box, so a "straight" member expression is returned.

如果您想要访问 UnaryExpression 中的 MemberExpression 您可以获得其操作数：

If you would like to get to the MemberExpression inside the UnaryExpression, you can get its operand:

private static MemberExpression GetMemberExpression<T>(
    Expression<Func<T,object>> exp
) {
    var member = exp.Body as MemberExpression;
    var unary = exp.Body as UnaryExpression;
    return member ?? (unary != null ? unary.Operand as MemberExpression : null);
}

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