Core Data Merge Conflict

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Created Jun ’20

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I've been struggling with trying to figure out why I'm experiencing merge conflicts when trying to save my managedObjectContext.

My app is using a single MOC on the main thread only. There are no background tasks being completed in Core Data. (User sees a fetched list of categories/items, can add to the list or delete from the list.) The app is seeded with data upon initial launch via a bundled SQLite file.

If I use a SQLite file with a small amount of records (~50) in one of the two tables, saving new objects w/ the MOC works fine. If I use the same SQLite file and add more records to that same table (~40,000) the app displays them fine but crashes upon trying to same the MOC. There error is:

Code=133020 "Could not merge changes" "...with oldVersion = 0 and newVersion = <deleted> and old cached row ="

The item cited in the error message is a random category/item each time and not the new category/item being saved w/ the MOC.

I've tried various merge policies although they all have the same effect: the new object is not saved. I'm puzzled why it appears that when the larger data set is being used CoreData thinks a completely different object is being deleted and fails to insert the new object.

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Answer 1

DeveloperStanTron OP

Jul ’20

Code example of how I get a MOC, set entity attributes, and save MOC:

Code Block let newCategory = Category(context: CoreDataStack.getContext())
newCategory.attribute1 = textField.text!
newCategory.attribute2 = true
CoreDataStack.saveContext()

getContext() simply returns a persistentContainer.viewContext and saveContext() is a basic:

Code Block if context.hasChanges {
						do {
								try context.save()
								
						} catch let error as NSError {
								let nserror = error as NSError
								fatalError("Unresolved error when saving MOC: \(nserror), \(nserror.userInfo)")								
						}
 }

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