Passing objects between managed object contexts

Question

Hi there,

I have an iphone app with 2 managed object contexts. One of my contexts deals with a picker, which allows the user to add new records and then select one of those new records. Once the picker is hidden, that managed object context is saved and discarded.

I then want to use this selected object in my second managed object context, and add (relate) it to another object. This second MOC's changes may be saved or deleted. This is why the first MOC is created to allow the changes made in the picker to always be saved no matter wether they save or discard the changes in the second MOC.

I hope this is clear! My problem is that when the user selects the object from the picker, this object resides in a different context to where it needs to be used. Is there a way you can pass objects between contexts? Perhaps using the object's ID (after it has been persisted).

Thanks for your help!

Answer 1

You mentioned the correct solution in the question. You cannot pass NSManagedObjects between multiple contexts, but you can pass NSManagedObjectIDs and use them to query the appropriate context for the object represented by that ID. So simply persist out the data (via a save:), and then pass the ID to the other context and use it to ask the context for the appropriate object.

Depending on what you want to do you may want to rig up the mergeChangesFromContextDidSaveNotification: so that changes in one context are automatically reflected in the other.