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handling data relations in Core Data
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handling data relations in Core Data


  • Subject: handling data relations in Core Data
  • From: Daniel Child <email@hidden>
  • Date: Mon, 16 Feb 2009 00:16:14 -0500

Hi All,

I'm working out some tests one one-to-many and many-to-many relations between entities. So far things are working well, including the bindings. But I'm puzzled by the documentation.

http://developer.apple.com/DOCUMENTATION/Cocoa/Conceptual/CoreData/Articles/cdRelationships.html#/ /apple_ref/doc/uid/TP40001857-SW3

The Core Data Programming Guide has this passage:

Since Core Data takes care of the object graph consistency maintenance for you, you only need to change one end of a relationship and all other aspects are managed for you. This applies to to-one, to-many, and many-to-many relationships....

Are they saying that if you set the relation in one direction, you don't have to bother doing the inverse?

Let's say I have two tables A and B with a 1:N relation.

Entity A (one table)
Adata (property)
relatedBItem (relationship)

Entity B (many table)
Bdata (property)
relatedAItems (relationship)

And here are some relations between managed objects having Adata values and Bdata values.

Table A	Table B
one 		a, b, c
two		a, b
three		d, e
four		f, g

Now let's say I'm setting the properties for "a" (an instance of Entity B). If I say that a's relatedAItem = @"one", then is Core Data going to automatically set one's relatedBItems to @"a"? If not, what do they mean by "all other aspects are managed for you"?

Thanks.

Daniel

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