Property Name to Lambda Expression C#

Question

How can I convert a property name to Lambda expression in C#?

Like this: string prop = "Name"; to (p => p.Name)

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

Thanks!

A lambda expression is not a type. Do you mean a delegate or an expression tree? And of *exactly* what type? — Lucas Trzesniewski, Aug 11 '15 at 17:49
I don't understand your question... You want to turn a variable declaration into a property access expression? — Matías Fidemraizer, Aug 11 '15 at 18:04
Please explain what you are trying to achieve. Converting a property name to Lambda does not really make sense. Add some context. — Pierre-Luc Pineault, Aug 11 '15 at 18:06
I have a Expression> param in a function, and I have only the property name, so I need to "transform" the property name into a Expression. — Renan Araújo, Aug 11 '15 at 18:10

Taher Rahgooy · Accepted Answer · 2015-08-11T18:27:19.870

26

Using expression trees you can generate the lambda expression.

using System.Linq.Expressions;
public static Expression<Func<T, object>> GetPropertySelector<T>(string propertyName)
{
    var arg = Expression.Parameter(typeof(T), "x");
    var property = Expression.Property(arg, propertyName);
    //return the property as object
    var conv = Expression.Convert(property, typeof(object));
    var exp = Expression.Lambda<Func<T, object>>(conv, new ParameterExpression[] { arg });
    return exp;
}

for Person you can call it like:

var exp = GetPropertySelector<Person>("Name");//exp: x=>x.Name

edited Aug 11 '15 at 18:27

answered Aug 11 '15 at 17:57

Taher Rahgooy

6,528
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1

This isn't reflection – Matías Fidemraizer Aug 11 '15 at 18:03
This works only for string. Is there a way to make the Expression.Lambda> generic? I've tryied Expression.Lambda> but didn't work. – Renan Araújo Aug 11 '15 at 18:15
I've change it to support generics. – Taher Rahgooy Aug 11 '15 at 18:19
I would say: "You can use **expression trees**" :D – Matías Fidemraizer Aug 11 '15 at 18:19
Some part of Expression tree is in fact based on Reflection. Looks like the `conv` is redundant here, you can just pass `property` in the `Expression.Lambda` instead of `conv` (tested and it works that way). – Hopeless Aug 11 '15 at 18:39
2

@Hopeless: Convert is required for value types, like int. Without it this exception is thrown: "Expression of type 'System.Int32' cannot be used for return type 'System.Object'" – Kamarey Apr 11 '18 at 08:36

score 1 · Answer 2 · answered Aug 11 '15 at 17:51

1

A lambda is just an anonymous function. You can store lambdas in delegates just like regular methods. I suggest you try making "Name" a property.

public string Name { get { return p.Name; } }

If you really want a lambda, use a delegate type such as Func.

public Func<string> Name = () => p.Name;

answered Aug 11 '15 at 17:51

Philippe Paré

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well yes, since it doesn't have a name to define its location. – Philippe Paré Aug 11 '15 at 18:07
And what about expression trees? Are them delegates too? :P – Matías Fidemraizer Aug 11 '15 at 18:20
To be fair, I'm not familiar with expression trees (if you're talking about Linq's Expression class), but I don't think it inherits from either Delegate or is a delegate type. – Philippe Paré Aug 11 '15 at 19:24
They're not delegates. They can compile to delegates – Matías Fidemraizer Aug 11 '15 at 19:25
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/86808/discussion-between-philippe-pare-and-matias-fidemraizer). – Philippe Paré Aug 12 '15 at 15:50

Property Name to Lambda Expression C#

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