I just can't find a solution for this. Basically, I need a pre-delete hook in CoreData but can't seem to find one.
Here's the deal - I have a Foo object which has many Bar objects. Foo also has a property that's calculated off of the various values in Bar. So Bar has many custom set<Key> methods that twiddle the value up in the Foo object to keep it up to date. All works well and good. The problem is if I delete a Bar object. I need a way to have the Bar object revert the cached Foo property to what it would've been had it never existed. Basically, a pre-delete cleanup hook. So what happens is, upon delete it marches through all of my set<Key> methods in some order to wipe them out and screws up my cached property. Basically, it ends up backing out the Bar object multiple times, since while it's knocking out all of the properties, it doesn't know that the object is actually deleted. Boom. Big mess. Problems and caveats: * I can't just have Foo monitor removeBarObject because it's not guaranteed to wipe out the relationship first. It may have called a half a dozen custom set<Key>s in Bar first so I'm still in some inconsistent state. * I have to have Bar notify Foo of changes (as opposed to having Foo observe all of Bar's related properties) since there are relatively few Foo objects and a -lot- of Bars. Further, the Bars only rarely change their value. So to have a few Foos monitoring tons of Bars all the time is just going to create a whole bunch of additional overhead that I don't want. * I have to store the property up in Foo, since it can also be manipulated via other means. That is, I can't just replace the calculated property with keyPath monitoring of the Bars. * validateForDelete is called way too late in the process. I watched it. It's very helpfully called after my object data is wiped out, all of my set<Key>s are called, and my object's a mess. * likewise for isDeleted. Doesn't work as a flag. Possibilities: * I can add an explicit "flagForDeletion" method to my Bar object and explicitly call this every time I'm going to delete one. This seems error-prone to me, since I may forget to put it somewhere. Further, it makes it difficult to use in abstract situations unless I add dummy flagForDeletion flags to all of my objects just to ensure that I can always call the method. I know I can do it with a category, but still. Likewise, I can add that into my ArrayController to handle the majority of the cases. For now, I've gone with that approach. the ArrayController's removeObjectAtArrangedIndex: method calls flagForDeletion, which for most objects does nothing, but for the Bars properly updates Foo's property and then flags them as trash so the set<Key> values won't update. I hate having the extra method, though. Is there any better approach I can use? With in the constraints of the above caveats, of course. -Jim... _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
