I've got two objects in my data model, say Class and Teacher. Class
has a to-one relation to a Teacher and Teacher has a to-many back to
Class.
When a Class is created I assign a particular default Teacher to it
(e.g. J. Doe). Then, J. Doe has that class added to his set of
Classes. I override [Class setTeacher:] to change a nil Teacher to
the default Teacher.
- (void)setTeacher:(Teacher *)teach
{
if (teach == nil)
// from my NSManagedObjectContext extensions
teach = (Teacher *)[[self managedObjectContext] fetchOne:@"Teacher"
whose:@"name" is:@"J. Doe" createIfNone:NO];
[self willChangeValueForKey:@"teacher"];
[self setPrimitiveValue:teach forKey:@"teacher"];
[self didChangeValueForKey:@"teacher"];
}
This works great and every class starts with J Doe and if a Class's
Teacher is set to nil, then it gets J Doe (who works very hard).
There is, of course, one small problem that happens when a Teacher is
remove:'d from the object model. The Delete Rule for Teacher.Class is
set to Nullify. When a Teacher is removed, all of it's Classes get
their Teacher set to null, which is overridden in setTeacher: so each
Class gets J Doe for its Teacher. The problem is that this is not
reflected in Teacher -- the Class is not added to the J Doe's set of
Classes.
Bottom line:When a Teacher is remove:'d, its Classes get sent a
setTeacher:nil (because the Delete Rule is Nullify). The nil gets
changed to J Doe, so the Class points to J Doe. But J Doe is not
updated to point back to Class.
Am I not supposed to modify the object graph during a remove:? Or, is
this a bug in Delete Rule handling that I should submit? Or, did I
miss something in the docs about this situation?
Thanks.
john
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