NHibernate Linq Query Where(x => x is Base Class) doesn't get derived objects

Question

Let's say I have the following structure, mapped with a discriminator (Table per hierarchy):

    Entity (abstract, no discriminator)
      |
    Animal (abstract, no discriminator)
    /    \
Dog (1)  Cat(2)

If I query on this using Linq to NHibernate:

.Where(x => x.Entity is Animal)

I get no results. When looking at the generated query I expected to see:

where type in (1, 2)

But instead I got this:

where type='animal'

Animal is abstract and doesn't even have a discriminator, so the generated query is meaningless.

Digging a bit deeper I found that the query is translated internally to something similar to WHERE x.class=animal in HQL. Is this a bug in Linq to NHibernate? Or is it expected behavior?

Answer 1

I fixed this bug added this feature to NHibernate. The changes are here and can be built from source. I issued a pull request so hopefully this will be working soon.

Update : It was merged , and should be available in the next release.

Answer 2

Do you get expected result when using

session.Query<Animal>().Select(a => a.yourXEntity).ToList()

Or

session.Query<Animal>().SelectMany(a => a.yourXEntityCollection).ToList()

instead? Those one should handle polymorphism.

While your lambda x.Entity is Animal gets very likely translated to HQL x.Entity.class = Animal which does not handle polymorphism and takes only the discriminator value of specified class, which defaults to its class name.