如何使用反射在運行時構建此c＃“Expression”？

Question

直到今天，我還沒有找到一篇關於表達的好文章 - 以及如何查看C＃lambda語句並說“哦，那是一個等等等等......”所以，如果你知道一篇好文章，我會很感激這也是一個答案。

代碼示例解釋問題

所以...給出以下c＃代碼：

public class SomeClass<T>
{
    public TResult SomeMethod<TResult>(Expression<Func<T, TResult>> expression)
    {
        // This is just an example... don't get hung up on this :)
        return default(TResult);
    }
}

public class Person
{
    public string FirstName { get; set; }

    public string LastName { get; set; }
}

我該怎么做呢...

var blah = new SomeClass<Person>();

blah.SomeMethod(p => p.FirstName);

在運行時（使用反射）？

我期待作為答案

我有點期待這樣的事情...但我確信我選擇的表達方式已經過時了。

// By the way, these values are being passed to me... so you
// can't change this part of the question :)
Type personType = typeof(Person);
string propertyName = "FirstName";

// THIS CODE BELOW IS OBVIOUSLY WRONG, BUT YOU GET THE IDEA OF
// WHAT I HOPE TO DO... THIS LINE OF CODE BELOW IS **ALL** I'M
// ASKING HOW TO DO :)
var expression = Expression.MakeUnary(ExpressionType.Lambda,
    Expression.Property(Expression.Parameter(personType, "p"),
    propertyName), typeof(string));

blah.SomeMethod(expression);

Answer 1

試試這個：

var functorParam = Expression.Parameter(typeof(Person));
var lambda = Expression.Lambda(
    Expression.Property(functorParam, typeof(Person).GetProperty("FirstName"))
,   functorParam /* <<= EDIT #1 */
);
blah.SomeMethod((Expression<Func<Person,string>>)lambda); /* EDIT #2 */

Answer 2

ExpressionBuilder是要走的路。