Currently, when using a hierarchy of types (Animal -> Cat, Dog), it is required to always use the base class as the generic type on collection (Animal).

That's fine, but if I only want to then work with Cats, I must add the discriminator in manually to every filter. There should be a way to do this automatically.

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There is currently a commit here (https://github.com/craiggwilson/mongo-csharp-driver/tree/oftype) that adds a method called OfType to IMongoCollection<T> which does this exact thing. It includes the discriminator with every filter.

For instance, `db.GetCollection<Animal>("animals").OfType<Cat>();` returns an IFilteredMongoCollection<Cat>, which implements IMongoCollection<Cat>. From here, everything that can be done on a normal collection can be done on this collection, except the discriminator will be added to all filters.