We just ran into this limitation which is having an impact on what we can do with Morphia. Also referenced on stack overflow: http://stackoverflow.com/questions/21921442/getting-multiple-types-from-same-morphia-query

Any interest in this now? It looks like this original ticket is from 2010. :(

Interest, yes. The timing is uncertain. Probably post-1.0 at this point. The C# driver has an interesting solution i'll probably steal but it'll take some refactoring first.

This is major for me as well. I'm facing a lot of issues and having to resort to direct driver use to work around these issues as Morphia does not play nicely with polymorphic structures.

Say, if one has class A and B and C that inherit from them it seems natural that A could be annotated with @polymorphic and all instances of A, B and C would then go to the A's collection. For each record, I like the idea of storing an array of class names going up in the type hierarchy for stored objects instead of the fully qualified name for the concrete implementation classes stored. This way one could query for instances of A, B, C or a combination of them and have them properly filtered and casted.

This is a major limitation and a bit discouraging to see it open from 2010... it's been 5 year after all :(

Just as a side not if anyone is interested in a work around, as for the example above instead of querying for
datastore.find(Circle.class)

...I am instead querying for:

datastore.createQuery(Circle.class).disableValidation().filter("className =", Circle.class.getCanonicalName()).asList();

which works well but is a bit ugly. Also I don't know if we add an index to the className field but if we don't then this could make this query very slow for large data sets.

+1 to issue

+1

+1 or is this closed i.e. implemented already?

+1

any progress about this one?

I know this ticket is pretty old but I just wanted to provide an alternative.
Have a look at Polymorphia
Among other things Polymorphia adresses the need to persist polymorphic data structures.
It is based on the java mongo driver and adds a codec to support POJOs.
Also generic classes are supported. Polymorphia provides fine grained control over discriminator handling within the mongo database.
Give it a try and let me know, what you think.

Any opinions or progress about this issue? Otherwise we can start the 5 year celebration - if it didn't take place already ;-) Thanks @webermich for your effort, but changing the mapping to a different mechanism is not possible for me at the moment.

I actually have this done in my fork that I'm working on. I've replaced the mapping code with the driver's POJO stuff i helped write. It's getting pretty close to done.

@evanchooly any update on this?

+1 🥇

working now in 2.0 though the @Polymorphic annotation isn't necessary.

@evanchooly Can you please explain how this should work in Morphia 2.4.2?

I tried:

// ... Junit setup...

	@Entity("shapes")
	public static class BaseShape {
		@Id
		protected ObjectId id;
		protected int sides;
	}

	@Entity("shapes")
	public static class Circle extends BaseShape {
		{ sides = 0; }
	}

	@Entity("shapes")
	public static class Triangle extends BaseShape {
		{ sides = 3; }
	}
	
	@Test
	void minimalTestCase() {
		log.info("Starting test");
		var ds = datastore();
		ds.getMapper().map(BaseShape.class, Circle.class, Triangle.class);
		ds.save(new Circle());
		ds.save(new Triangle());
		log.info("Trying to find shapes");
		ds.find(BaseShape.class).forEach(s -> {
			log.info("Found: " + s);  // --> nothing was printed from here
		});
		log.info("These were all the shapes");
	}

If I save an instance of BaseShape - then that can be found. If I search for any of the child types, I find only instance of that specific sub-type.

You have to enable polymorphic queries. But please open a discussion topic rather than comment on 10 year closed issues so that folks aren't notified unnecessarily.