create entity in child NSManagedObjectContext with relationship to parent entity

Question

I am creating temp context for edit entity:

    NSManagedObjectContext *parent = [Default managedObjectContext];//my main managed context
    NSManagedObjectContext *_createNewContex = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
    [_createNewContex setParentContext:parent];

In the _createNewContex I am trying to create My temp entry for editing.

   MyTempEntry *entry = [MyTempEntry createInContext:_createNewContex];

It is created ok but if try to assign relationship for entry from parent context:

  entry.entryFromParent = parentEntry;

I have error:

* Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Illegal attempt to establish a relationship 'entryFromparent' between objects in different contexts

Answer 1

you can't use object's between context's. you'll need to lookup the object on the secondary context using its objectID, or some other value.

that object from the secondary context can then be used to create the relationship.

something like the rough code below

NSManagedObjectID *objectID = [parentEntry objectID];

id newContextParentEntry = [_createNewContext objectWithID:objectID]; 

entry.entryFromParent = newContextParentEntry;