NHibernate Overcoming NotSupportedException

Question

Does anyone know of any way to overcome NotSupportedException? I have a method against a User:

 public virtual bool IsAbove(User otherUser)
 {
     return HeirarchyString.StartsWith(otherUser.HeirarchyString);
 }

And I want to do:

_session.Query<User>.Where(x => loggedInUser.IsAbove(x));

But this throws a NotSupportedException. The real pain though is that using

_session.Query<User>.Where(x => loggedInUser.HeirarchyString.StartsWith(x.HeirarchyString));

works absolutely fine. I don't like this as a solution, however, because it means that if I change how the IsAbove method works, I have to remember all the places where I have duplicated the code whenever I want to update it

Elwoodelwyn

ah crap, i'm always the first to point out when people can't spell too! must've been getting that one wrong for years :$ – Elwoodelwyn

Answer 1

Name the specification expression and reuse that, e.g:

public Expression<Func<....>> IsAboveSpecification = (...) => ...;

public virtual bool IsAbove(User otherUser)
{
    return IsAboveSpecification(HeirarchyString, otherUser.HeirarchyString);
}

Reuse IsAboveSpecification in the query as needed. If the IsAbove() method is used often use can cache the result of the Compile() method on the expression.

Vaduz

I'm having the same issue as OP. Can't get this solution to work. In the first place, I want to be able to call on the object, so I had to move the initialization into the constructor because this was not available in a member initializer. Worse, I'm getting an error when trying to call the specification expression: "Method, delegate or event expected". Any suggestions? – Tran

Tried calling .Compile().Invoke() on the expression. It compiles now, but getting the same exception when calling the function "IsAbove" from a query. – Tran

Can't call the expression from the query for several reasons: first, when it is marked as public, NH complains that fields must be protected or private. Second, when I tried calling it from an external query I got the same "Method, delegate or event expected" compiler error as above. – Tran

You should ask a new question and post the code you are attempting to use. I don't think NH would complain about something being public - it does insist that the virtual modifier is present though. – Vaduz

Thanks for the suggestion. Kind of moved on for the moment, but I'm sure we will come back to this. I'll ask a new question when this becomes relevant again (it will!). – Tran