I am using Apple's CoreDataBooks sample application as a basis for pulling data into a secondary managed object context in the background, and then merging that data into the primary managed object context.
The data I am pulling in is a Book entity with a to-one relationship with an Owner entity (called "owner"). The Owner entity has a to-many relationship with the Book (called "books").
My data is an XML document of the form:
<Owner>
<Name>alexpreynolds</Name>
<ID>123456</ID>
</Owner>
<Books>
<Book>Book One</Book>
<Book>Book Two</Book>
...
<Book>Book N</Book>
</Books>
Book One through Book N are associated with one Owner ("alexpreynolds, 123456").
I am parsing this into an Owner instance and an NSMutableSet made up of Book instances.
When I attempt to save the first time, it saves fine and the merged data shows up in the table view.
On the second save, however, when the XML content contains a new book, it doesn't work.
Here's what happens:
I then attempt to load in an XML document that contains a new Book not already in the primary managed object context. The new Book is using the same Owner as that which is associated with the other Books.
I have routines that pick out this unique Owner managed object (which I already have in my primary managed object context) and the unique Book that is not found in the primary MOC.
From this, I create a new Book object in the secondary MOC, and I set its "owner" relationship to point to the unique Owner I found in the primary MOC.
When I save, I get the following error:
*** Terminating app due to uncaught
exception 'NSInvalidArgumentException',
reason: 'Illegal attempt to establish a
relationship 'owner' between objects in
different contexts
(source = <Book: 0x7803590>
(entity: Book; id: 0x7802ae0 <x-coredata:///
Book/t527F06B2-3EB5-47CF-9A29-985B0D3758862>
; data: {
creationDate = 2009-10-12 06:01:53 -0700;
name = nil;
nameInitial = nil;
operations = (
);
owner = nil;
type = 0;
}) ,
destination = <Owner: 0x78020a0> (entity:
Owner; id: 0x3a56f80 <x-coredata://043AF2F0-1AD0-
4078-A5E8-E9D7071D67D1/Owner/p1> ; data: {
books = "<relationship fault: 0x7801bf0 'books'>";
displayName = alexpreynolds;
ownerID = 123456;
}))'
How do I create a new Book entity in the secondary MOC, so that I can still associate it with a pre-existing Owner in the primary MOC?