NSManagedObject changed properties after save

Question

Is it possible to find out which properties were saved on a managed object after the save occurs? For example, I have someone listening for managed object context saves, (NSManagedObjectContextDidSaveNotification) and I want to know which properties on the objects were saved.

Answer 1

The NSManagedObjectContextDidSaveNotification does contain all three bits of information you would need to sync with a server. Check the [notification userInfo] and you will find three sets inside: NSInsertedObjectsKey, NSUpdatedObjectsKey, and NSDeletedObjectsKey

If you want to know what properties on an entity have changed that would require that you track them yourself using KVO. I would recommend against this as the odds of that level of effort being worth it over just pushing the entire object up to a server are slim.

Update #2

On further poking around:

From the NSManagedObjectContextWillSaveNotification you could loop through each set and reference the changedValues method. You could keep a reference to that dictionary until after you receive the NSManagedObjectContextDidSaveNotification and then process the changes. Still sounds very heavy to me.

Update

What is your end goal?!?!

If you are trying to figure out what to push to a server then being at the attribute level is too low. You should be syncing at the entity level.

If you are just trying to keep some internal consistency inside of your application then you are thinking way, way too low level. This is a solved problem. Core Data solved it.

Answer 2

Why don't you get them when they are about to be saved. Subscribe to NSManagedObjectContextWillSaveNotification and check insertedObjects, updatedObjects and deletedObjects of the NSManagedObjectContext.

Update:

Even easier, get the user info of the NSManagedObjectContextDidSaveNotification

From the documentation:

Typically, on thread A you register for the managed object context save notification, NSManagedObjectContextDidSaveNotification. When you receive the notification, its user info dictionary contains arrays with the managed objects that were inserted, deleted, and updated on thread B.

http://developer.apple.com/library/ios/#documentation/cocoa/conceptual/coredata/Articles/cdConcurrency.html#//apple_ref/doc/uid/TP40003385-SW1