Linq to SQL writing translatable functions

Question

I'm pretty sure the answer to this is "you can't do that" or "No, no, you misunderstand...", but:

I have a linq class, thing, which will happily execute this:

 var thingsWithAandB = from t in db.things
                       where t.propA.HasValue && t.propB.HasValue
                       select t;

But I do this a lot, and so I want:

partial class thing
{
    public bool hasAandB
    {
        get
        {
            return propA.HasValue && propB.HasValue;
        }
    }
}

and then:

var thingsWithAandB = from t in db.things where t.hasAandB select t;

But of course, when I do this, I get "Can't translate that into SQL" errors. And I understand that this is because calling methods in the middle of SQL queries isn't possible, since my code and the database are separate.

What's the way to do this? Is it impossible?

Answer 1

It is perfectly possible. Damien Guard (damieng.com) has a sample on his blog showing how to do that.

http://damieng.com/blog/2009/06/24/client-side-properties-and-any-remote-linq-provider

Answer 2

You can use extension methods:

public static class MyExtensions{
    public static bool HasAandB(this thing t){
        return t.propA.HasValue && t.propB.HasValue;
    }
}

and then use it:

var thingsWithAandB = from t in db.things
                   where t.HasAandB()
                   select t;

EDIT
Sorry, this will probably give you the same exception...