Relationships and entities in CoreData?

First, it'd be easier to discuss your situation if you'd avoid using be to mean several different things. There are four relationships in your diagram; for the sake of the discussion, you could name them d e f and g.

First, it'd be easier to discuss your situation if you'd avoid using be to mean several different things. There are four relationships in your diagram; for the sake of the discussion, you could name them d, e, f, and g. To answer your question, you can't and don't need to include the kind of restriction that you're talking about in the model.

The model defines relationships between kinds of managed objects, but it doesn't say anything about individual objects. It's usually better to try to think in terms of objects when you're learning Core Data, but you should know that the entities you define in the model are analogous to tables in a relational database: they define can be stored, not what the code should or must (or must not) store. To restrict C.

A to one of the A's in C.b. Bs, you'll need to write some code. If C.

A is only set in one place, you might choose to implement the restriction in that code. If the restriction is essential to the proper operation of C, you might instead (or in addition) choose to add a check to the setter for C. A that verifies that the A is one of the allowed ones.

You may also need to fix up the setter for C. B so that if C. B changes, it verifies that C.

A is still valid and does something appropriate if it's not (clear C. A, pick a new C. A, refuse to accept the new C.

B, post a notification, throw an exception, whatever).

Thank you, how can I override the setter, normally I would just right my own setter. But CoreData must do something more than a normal setter (else why use @dynamic? )?

– Jonathan. Nov 19 '11 at 17:26 @Jonathan. See this question to learn how to write a your own Core Data setters.

Apple's documentation also talks about customizing Core Data accessors. – Caleb Nov 20 '11 at 4:06.

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