Retrieving Master from Slave
Retrieving Master from Slave
- Subject: Retrieving Master from Slave
- From: Mike Rossetti <email@hidden>
- Date: Mon, 28 Jan 2008 22:17:25 -0700
The following refers to a Core Data document-based application with a
'Master' entity that has a many-to-one relationship to a 'Slave'
entity. The Master is the root entity of the document. I', building
to 10.5 and my implementation is nearly identical to the one
demonstrated in the "NSPersistentDocument Core Data Tutorial".
At the point of my question, the document object has been retrieved
from disk and I am editing by adding a new Slave to the existing
Master entity. In Slave's awakeFromInsert I would like to retrieve
the Master and initialize some attributes in the new Slave entity
using attributes from the Master.
I'm a little confused as to how retrieve a reference to the Master. I
originally thought that I could just use self.master or [self
valueForKey:@"master"] but the 'master' member is nil. Re-reading the
"Adopting the Mediator Pattern" in the "NSPersistentDocument Core Data
Tutorial" made me try fetching the Master using an
executeFetchRequest, which works. The tutorial suggests that simply
retrieving the master from the relevant object controller is even more
appropriate but makes me wonder how the slave is supposed to get a
reference to the master entity object controller.
This seems like a lot of work and I can't help but think that there is
a simpler way to retrieve the 'master' object.
Any suggestions? Examples?
Thanks,
Mike
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