Re: Coredata schema question.
Re: Coredata schema question.
- Subject: Re: Coredata schema question.
- From: Scott Ellsworth <email@hidden>
- Date: Wed, 1 Jun 2005 11:23:21 -0700
On May 31, 2005, at 11:42 PM, Chris Hanson wrote:
On May 31, 2005, at 9:09 PM, James Andrews wrote:
I want to be able to link Photographs to Albums, and want to be
able to put the same image in multiple Albums. I had thought
maybe another Entity between Albums and Photographs, but I am not
sure if that would work the way I would expect it too.
Suggestions on how to do it, and explanations on why you would do
it that way would greatly appreciated.
That's how you would do it in a database — you would use a many-to-
many correlation table. However, with Core Data you're working
with entities and relationships so you can simply declare that your
Photograph.albums relationship and Album.photographs relationship
are both to-many and are each others' inverses. Core Data will
take care of the rest.
Beware - Core Data can suffer some major speed problems with many-
many relationships, especially on SQL stores. DTS convinced me to
remove my many-to-many relationships for performance reasons.
(If this bugs you, file a bug - I did.)
That said, it is not likely to be a problem for small data sets. I
have ~5k entities, of which half were in one group, a quarter were in
two, and a small number were in three or more. With 100 entities,
performance was snappy.
Scott _______________________________________________
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