Question

I’m having some problems running a LINQ query off of a LINQ2SQL class that inherits from a base abstract class.

[DataContract]
public abstract class AbstractClass
{
    [DataMember]
    public abstract int Foo { get; set; }
}


// LINQ2SQL class.
[DataContract]
public class ConcreteClass : AbstractClass
{
    [DataMember]
    public override int Foo { ... }
}

The problem occurs when I try to run a LINQ query against my Concrete Class. I get a SystemException saying, “Class member AbstractClass.Foo is unmapped.” The query would look something like the following:

// Sample LINQ query.
result = from c in dataContext.ConcreteClasses where c.Foo == 42 select c;

Notice how the query is against CocnreteClass, but the error is on the AbstractClass. Any ideas whats going on here?

Answer 1

It looks like the compiler was having problems infering the correct type. Instead of using the class returned by the LINQ2SQL context, it was using the base class, so I had to cast it to the correct type explicitly.

This previous example does NOT work:

result = from c in dataContext.ConcreteClasses where c.Foo == 42 select c;

This example does work:

result = from c in dataContext.ConcreteClasses where ((ConcreteClass)c).Foo == 42 select c;

Odd, but it works. Upvotes to anyone who can figure out why it would do that.

(Reference: Very strange inheritance behavior.)