Object Identity Tests in Core Data
Object Identity Tests in Core Data
- Subject: Object Identity Tests in Core Data
- From: Niko Matsakis <email@hidden>
- Date: Tue, 30 Aug 2005 15:45:05 +0200
I am building on the excellent Core Data framework and I have a
question. It often happens that I would like to build a query where
I want to find all entities with a reference equal to a given
object. Is there a good way to do this?
Allow me to use an example to clarify because I can't even understand
what I wrote in that previous paragraph:
Let's say I have an application with two types of entities: Word and
User. Each Word has a relationship "user" that indicates which user
it is associated with. I now want to select for the current user the
set of all of the words associated with them.
As far as I can tell, the predicate language doesn't really work with
pointers as much as strings and scalar fields. So, the way I do this
today is to require that each user have a unique name, and then
encode a fetch request for Word entities with a predicate like:
"user.name == $USERNAME"
and in my code I ensure that $USERNAME is bound to [userObject
valueForKey:@"name"].
What I would like to do is to instead use object references so that
there are no assumptions about whether or not the names are unique.
For example, I might do:
"user == $USEROBJECT"
and bind $USEROBJECT to userObject in my code.
Will this work? If not, is there a way to do what I want? Is my
question clear?
Thanks in advance.
Niko
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