NSFetchedResultsController on a one
I am implementing an NSIncrementalStore and I need to perform a paginated fetch and maintain the order of the elements within the request, then display the results in a table and maintain an NSFetchedResultsController associated with the query. I will try to explain my self better with an example
I have two entities, Entity1 and Entity2. Entity1 has a one-to-many relationship with Entity2 and since the fetch implies too many objects I want to perform a paginated request. I need to maintain the order of the objects arriving from the server so the objects are stored in an NSOrderSet . There is no inverse relation between Entity2 and Entity1.
The problem I am having is that I don't know how to instantiate the NSFetchRequest in this case.
I've read about pre-fetched relationships using setRelationshipKeyPathsForPrefetching but the NSFetchRequest its instantiated with Entity1 as entity ( [fetchRequest setEntity:[Entity1 class]] ) in all examples I read. I need a set of Entity2 objects.
Another idea was to use a fetched property but since I can't (and I don't want to) perform a sort on the request, I discarded it.
I hope I was clear and thanks Marcus Zarra in advance for encouraging me to ask this question.
Thanks a lot.
First, you need an inverse relationship. Core Data really should require them instead of just a warning. With an inverse this question becomes simple. Without an inverse it is all but impossible.
Assuming you add the inverse (as you should :) then you set up your NSFetchRequest against Entity2 with a predicate of "entity1 == %@" and you will get your results back. From there you can adjust the NSFetchRequest to handle the pagination.
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