RavenDB Inheritance

posted on 10 Dec 2011 | RavenDB

Note: Updated solution: http://www.philliphaydon.com/2011/12/ravendb-inheritance-revisited/

Continuing my learning of RavenDB, I wanted to see how it handled Inheritance.

I found: http://ravendb.net/faq/polymorphic-indexes

Which showed what to do allow you to select over all types of Animal for the example shown. So I wanted to see what happens before and after using this method.

So like the example shown I've created an Animal, with a Dog and Cat.

public abstract class Animal
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class Dog : Animal { }

public class Cat : Animal { }

Now if I insert a Dog and Cat:

using (var session = documentStore.OpenSession())
{
    session.Store(new Dog() { Name = "Test Dog" });
    session.Store(new Cat() { Name = "Test Cat" });
    session.SaveChanges();
}

What's stored in RavenDB is two separate documents, one for 'dogs' and one for 'cats'.

If I include the Convention.

var documentConvention =
    new DocumentConvention()
        {
            FindTypeTagName =
                type =>
                    {
                        if (typeof (Animal).IsAssignableFrom(type))
                            return "animals";
                        return DocumentConvention.DefaultTypeTagName(type);
                    }
        };

Note: You can do the conversion when the DocumentStore is initialized, I broke the two up so that it would fit easier into my blog. Otherwise it's too nested and yucky.

var documentStore =
    (new DocumentStore()
            {
                Url = "http://localhost:8080",
                Conventions = documentConvention
            }).Initialize();

Now when I insert a Dog and Cat I get:

Awesome. If we look at the document however:

There is no information about it being a cat or dog, I thought it would add some sort of discriminator similar to how NHibernate works.

However, if we look at the Metadata tab:

We can see the CLR type is stored in the metadata so RavenDB knows what type to create when we query it.

This means if we query for Animal we get a list of Dogs and Cats.

using (var session = documentStore.OpenSession())
{
    var result = session.Query<Animal>();
    foreach (var animal in result)
    {
        Console.WriteLine(animal.Name);
    }
}

However, if you wanted to query for just Dogs, like so:

var result = session.Query<Dog>().ToList();

It doesn't seem to work :(

I'm probably just doing something wrong, either way, the more I play with RavenDB. The more I love it.