iphone - Xcode consistency error: Setting the No Action Delete Rule... is an advanced setting -

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after creating data model in xcode, it's throwing following error each of object relationships:

consistency error: setting no action delete rule on [object relationship] advanced setting

what xcode trying tell me, , how should respond?

core data uses inverse relationships , delete rules keep object graph consistent

let's have a.foo <1—1> b.bar , a.foo = b. automatically (effectively) performs b.bar = a.

now let's [b delete]. "nullify" rule, b.bar.foo = nil. "cascade", [b.bar delete]. "no action", nothing; a.foo "dangling core data object reference".

it's not dangling pointer; standard memory management rules mean b still exist in memory while a points (until a turns fault), a.foo forever refer deleted object, raises exception when try access properties. i'm not sure happens when save , re-fetch a either.

with many-to-many relationship, gets more complicated. implementation details: relationship appears "owned" one of entities, , saved when entity saved (i hit bug when trying set relationship across different mocs: moc saved didn't own updated entity, relationship never saved). when delete both a , b, relationships should removed, 1 assumes relationship disappears 1 of them removed (but don't know one!).

you want nullify or cascade. never use cascade because can never remember direction cascading happens in.


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