Pass a property of a Linq entity in a method to set and get result

Question

I'm trying to pass in a property of a Linq entity to be used by my method. I can easily pass a property to be queried

Func<Entities.MyEntity, ResultType> GetProperty = ent => ent.Property;

However this returns ResultType and cannot be used to set the property.

I thought about using reflection to get a propertyInfo, but this will let me fetch the property but then I can't use Linq syntax to call my property. Is there any guru out there that knows how to do this?

I have a hunch I could do it by constructing a chunk of an expression tree and applying it onto the query...

I was really hoping to do something like:

var value = myQueryEntity.CallMagicFunction();  //typesafe
myQueryEntity.CallMagicFunction() = value; //typesafe

Answer 1

Indeed, an expression tree should work; for basic member access (a field/property directly off the object):

static MemberInfo ReadMember(LambdaExpression expr)
{
    if(expr == null) throw new ArgumentNullException("expr");
    MemberExpression me = expr.Body as MemberExpression;
    if(me == null || !ReferenceEquals(me.Expression, expr.Parameters[0])) {
        throw new ArgumentException("expr");
    }
    return me.Member;
}

with

Expression<Func<Customer, int>> func = c => c.Id;
MemberInfo member = ReadMember(func);
// for simplicity assume prop:
PropertyInfo prop = (PropertyInfo)member;

From there you can do pretty much anything; in particular you can get the get/set accessors (if you want to create a delegate), or use GetValue / SetValue.

Note that in .NET 4.0 you can set properties directly on an Expression (but the C# compiler doesn't add any extra support for this, so you'd need to write your own Expression by hand).