Order entities in Core Data data model

Question

I am using Core Data in my application, and I have entities that need to be reordered. I have a collection view that is populated with NSManagedObjects from the data model, and this collection view can be reordered by dragging and dropping the cells. I want the order of the entities in the data model to reflect the order of the cells in the collection view. Does anyone know how I can accomplish this? I am new to Core Data, so I am still getting used to it.

Answer 1

If I understand your question correctly, you may do it simply as follows:

• add an attribute viewOrder to your entity, probably an integer type
• update it any time the user drags and drops a cell, i.e. re-orders the collection view (& make sure to save: the NSManagedObjectContext whenever you make any changes)
• when populating the collection view, set the NSFetchRequest property sortDescriptors to sort the results by viewOrder
• note that if you add new managed objects, you'll have to run a fetch to count the current number in core date or to find the max viewOrder