Core Data: Abstract Entity in Fetch Request?

You can definitely use that approach. From Apple's Core Data Programming guide (scroll to the bottom section of the article): If you define an entity inheritance hierarchy (see “Entity Inheritance�), when you specify a super-entity as the entity for a fetch request, the request returns all matching instances of the super-entity and of sub-entities. In some applications, you might specify a super-entity as being abstract (see “Abstract Entities�).

To fetch matching instances of all concrete sub-entities of the abstract entity, you set the entity for fetch specification to be the abstract entity. In the case of the domain described in “Abstract Entities,� If you specify a fetch request with the Graphic entity, the fetch returns matching instances of Circle, TextArea, and Line.

Thank you! (My apologies for missing that part of the docs. After a few hours, they all start to run together.) – Bryan Jun 14 at 3:50.

I've done something similar, however that entity was not abstract. It was a standard entity (with no instances) and the other entities that I fetched were all derived from that entity. I haven't tried it with an abstract class, however, looking at the docs it appears that it might not be possible: Core Data Programming Guide Abstract Entities You can specify that an entity is abstract—that is, that you will not create any instances of that entity.

You typically make an entity abstract if you have a number of entities that all represent specializations of (inherit from) a common entity which should not itself be instantiated. For example, in a drawing application you might have a Graphic entity that defines attributes for x and y coordinates, color, and drawing bounds. You never, though, instantiate a Graphic.

Concrete sub-entities of Graphic might be Circle, TextArea, and Line. My suggestion would be to set things up with the abstract Animal entity and give it a shot. If it doesn't work then just make the Animal entity non-abstract (words are failing me, is that what we would call it?

Perhaps 'concrete' is better? ) and you should be fine. If anyone has done this with an abstract class I would to hear about it.

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