防爆pression的类型成员产生不同的防爆pressions（MemberEx pression，UnaryEx pression） [英] Expression for Type members results in different Expressions (MemberExpression, UnaryExpression)

问题描述

说明

我有一个EX pression指向我的类型的属性。 但它并不适用于每个属性类型的工作。 并不意味着手段 这导致不同的EX pression类型。我觉得它永远不会导致 MemberEx pression ，但事实并非如此。

有关 INT 和的Guid 这会导致一个 UnaryEx pression 和字符串 在 MemberEx pression 。

我有点糊涂;）

部分样品code

我的类

 公共类Person
{
    公共字符串名称{;组; }
    公众诠释年龄{获得;组; }
}
 

测试code

 者P =新的Person {年龄= 16，名称=约翰};

防爆pression＆LT; Func键＆LT;人，对象＆gt;＆GT; EX pression1 = X =＆GT; x.Age;
// EX pression1.Body = UnaryEx pression;

防爆pression＆LT; Func键＆LT;人，对象＆gt;＆GT; EX pression2 = X =＆GT; x.Name;
// EX pression2.Body = MemberEx pression;
 

问题

我

如何比较两个EX pressions，并检查他们的平均 相同类型和相同的属性？

更新，接听和完整的示例

由于用户的 dasblinkenlight 谁把我在正确的轨道上。

他提供的方法

 私有静态MemberEx pression GetMemberEx pression＆LT; T＆GT;（
    防爆pression＆LT; Func键＆LT; T，对象＆gt;＆GT; EXP
）{
    VAR成员= expr.Body为MemberEx pression;
    VAR一元= expr.Body为UnaryEx pression;
    返回成员？ （一元= NULL unary.Operand为MemberEx pression：！？NULL）;
}
 

我写了下面的扩展方法来比较的结果 GetMemberEx pression 方法和检查 GetMemberEx pression（）。Member.Name 是相同的。

 私有静态布尔IsSameMember＆LT; T＆GT;（此例pression＆LT; Func键＆LT; T，对象＆gt;＆GT;表达式1，防爆pression＆LT; Func键＆LT; T，对象＆gt;＆GT ;表达式2）
{
    VAR RESULT1 = GetMemberEx pression（表达式1）;
    VAR结果2 = GetMemberEx pression（表达式2）;

    如果（RESULT1 == NULL || RESULT2 == NULL）
       返回false;

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

解决方案

出现这种情况的原因是，年龄是值的类型。为了强迫一个前pression返回值类型为 Func键＆LT;人，对象＆gt; 编译器需要插入的 转换（表达式的typeof（对象）） ，一个<一个href="http://msdn.microsoft.com/en-us/library/system.linq.ex$p$pssions.unaryex$p$pssion.aspx"><$c$c>UnaryEx$p$pssion.

有关字符串和其他引用类型，但也没有必要框，这样一个直当然成员pression返回。

如果你想获得的 MemberEx pression 在 UnaryEx pression ，你可以得到它的操作：

 私有静态MemberEx pression GetMemberEx pression＆LT; T＆GT;（
    防爆pression＆LT; Func键＆LT; T，对象＆gt;＆GT; EXP
）{
    VAR成员= expr.Body为MemberEx pression;
    VAR一元= expr.Body为UnaryEx pression;
    返回成员？ （一元= NULL unary.Operand为MemberEx pression：！？NULL）;
}
 

Description

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.

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

I am a little confused ;)

Some sample code

My class

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

Test Code

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;

Question

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

Update, Answer and complete Sample

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

He provided the method

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);
}

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;
}

解决方案

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.

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

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 = expr.Body as MemberExpression;
    var unary = expr.Body as UnaryExpression;
    return member ?? (unary != null ? unary.Operand as MemberExpression : null);
}

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