Inheritance in MongoDb: how to request instances of defined type

Question

This is how I used to utilize inheritance in Entity Framework (POCO):

ctx.Animals // base class instances (all instances)
ctx.Animals.OfType  // inher         


        

Answer 1

From your link:

The one case where you must call RegisterClassMap yourself (even without arguments) is when you are using a polymorphic class hierarchy: in this case you must register all the known subclasses to guarantee that the discriminators get registered.

Register class maps for your base class and each one of your derived classes:

BsonClassMap.RegisterClassMap();
BsonClassMap.RegisterClassMap();
BsonClassMap.RegisterClassMap();

Make sure that your collection is of type of your base class:

collection = db.GetCollection("Animals");

Find using your query. The conversion to the corresponding child class is done automatically:

var query = Query.EQ("_t", "Cat");
var cursor = collection.Find(query);