Identifying which fields have changed before CoreData saves

问题

//set up notifications

[[NSNotificationCenter defaultCenter]
 addObserver:self
 selector:@selector(dataChanged:)
 name:NSManagedObjectContextDidSaveNotification
 object:context];    

//later

- (void)dataChanged:(NSNotification *)notification{
  NSDictionary *info = notification.userInfo;
  NSSet *insertedObjects = [info objectForKey:NSInsertedObjectsKey];
  NSSet *deletedObjects = [info objectForKey:NSDeletedObjectsKey];
  NSSet *updatedObjects = [info objectForKey:NSUpdatedObjectsKey];

Is there anyway to determine from the updatedObjects which fields were actually changed?

thanks, Michael

回答1:

The following should do the trick, but you will need to use NSManagedObjectContextWillSaveNotification and access your updated objects through the same NSManagedObjectContext used to save the objects.

for(NSManagedObject *obj in updatedObjects){

   NSDictionary *changes = [obj changedValues];
   // now process the changes as you need

}

See the discussion in the comments.

来源：https://stackoverflow.com/questions/5976455/identifying-which-fields-have-changed-before-coredata-saves