Re: CoreData retain/release/delete

FROM : Bill Bumgarner
DATE : Fri Apr 29 23:46:12 2005

On Apr 29, 2005, at 1:22 PM, John Brownlow wrote:
> - (void) dealloc
> {
>    // regular dealloc stuff
>
>    [[self managedObjectContext] deleteObject: self];
> }
>
> It seems like it would work and is reasonably elegant, but it seems 
> a bit too obvious to be valid code! :)


The above would imply that you want to permanently delete the managed 
object from the store when the last reference to the object is released.

That seems like an odd design in that it is mixing business logic 
with generic object life cycle management.

If the managed object context is set to not retain registered objects 
-- which is the default -- then the deleted managed object should be 
reaped once all retains are cleared.  If it has been deleted and not 
saved, it will be reaped once the save occurs.

As Scott said, you really don't want to mess with Core Data's object 
life cycle management in the name of trying to manage your object graph.

It sounds like you probably want to set up an appropriate delete 
rule.  Most likely, you'll want to set the relationship to the 
object to use a cascading delete such that when the "owning" object 
is deleted, the destination object is also deleted.

> More importantly, what happens to the copy in the persistent store? 
> When the MOC saves, is the persistent store overwritten, and the 
> object effectively deleted from the saved file, or does it hang 
> around and have to be deleted manually using the -deleteObject method?


If you delete an object, it will be deleted from the store upon 
save.  Whether the store is overwritten is dependent upon what store 
you choose.  XML and Binary will atomically overwrite the store.  SQL 
will simply update the necessary rows in the store, deleting rows 
representing deleted object methods.

If you still have references to the deleted object and you save, the 
object will not be dealloc'd out from under you.  Instead, it will 
be turned into a fault that cannot be fired.  An attempt to fire it 
will cause an exception to be tossed.

b.bum