core data NSManagedObjectContext with NSMergePolicyType - Crash

Question

I added NSMergePolicyType for my context but every time that I have a conflict the app is crash.

I added constraints to the table in xcdatamodeld (with "id" )

This is my context:

lazy var managedObjectContext: NSManagedObjectContext? =
    {
        // Returns the managed object context for the application (which is already bound to the persistent store coordinator for the application.) This property is optional since there are legitimate error conditions that could cause the creation of the context to fail.
        let coordinator = self.persistentStoreCoordinator
        if coordinator == nil {
            return nil
        }
        var managedObjectContext = NSManagedObjectContext(concurrencyType: NSManagedObjectContextConcurrencyType.privateQueueConcurrencyType)
        managedObjectContext.persistentStoreCoordinator = coordinator
        managedObjectContext.mergePolicy = NSMergePolicyType.overwriteMergePolicyType
        return managedObjectContext
    }()

And this is the save:

func saveContext(onSuccess: (() -> Void)?) {
        if let moc = self.managedObjectContext {
            moc.perform {
                if moc.hasChanges {
                    do {
                        try moc.save()
                        onSuccess?()
                    } catch {
                        print("SaveContext error \(error)")
                    }
                }
            }
        }

But when i have a conflict with the id the app is crashed

• on the first entity created , everything work find
• but when i add entity with the same ID the app is crashed.

Error:

-[_SwiftValue resolveConflicts:error:]: unrecognized selector sent to instance 0x1d0256680

Core data logs:

CoreData: annotation: sql connection fetch time: 0.0001s
CoreData: annotation: total fetch execution time: 0.0001s for 1 rows.
CoreData: annotation: fault fulfilled from database for : 
0xd000000000080004 <x-coredata://E7F35452-965D-460D-AAFE-
5ED17B8E0174/DatapulseEntity/p2>
CoreData: sql: SELECT t0.Z_ENT, t0.Z_PK, t0.Z_OPT, t0.ZCREATEDTIME, 
t0.ZDELETEDTIME, t0.ZDESCRIPTION_VALUE, t0.ZID, t0.ZIS_MY_FAVORITE, 
t0.ZIS_SELF_LIKED, t0.ZIS_SELF_SAVED_OFFLINE, t0.ZIS_SELF_VIEWED, 
t0.ZIS_SHARED, t0.ZLIKES, t0.ZNAME, t0.ZPARENT_ID, t0.ZTHUMBNAIL, 
t0.ZTYPE, t0.ZUPDATEDTIME, t0.ZVIEWS, t0.ZLINKS, t0.ZREFRESHRATE FROM ZKNOWLEDGEBASEENTITY t0 WHERE  t0.Z_PK = ? 
CoreData: annotation: sql connection fetch time: 0.0000s
CoreData: annotation: total fetch execution time: 0.0000s for 1 rows.
CoreData: annotation: fault fulfilled from database for : 
0xd000000000040004 <x-coredata://E7F35452-965D-460D-AAFE-5ED17B8E0174/KnowledgeBaseEntity/p1>
2018-02-04 16:18:30.149318+0200[49571:18233278] -[_SwiftValue resolveConflicts:error:]: unrecognized selector sent to instance 0x1d0256680

Everting is working find , Only when i have an id conflict it crash. (try on iphone 8 , ios 11.2)

Answer 1

Found the issue:

The mergePolicy is a type of "Any" That means that you can insert any object widout getting an error.

BUT mergePolicy must get a mergePolicy object, any other object will cause a crash in the system.

What I have done is to pass the mergePolicyType and not the object.

Crash!:

managedObjectContext.mergePolicy = NSMergePolicyType.overwriteMergePolicyType

Work:

managedObjectContext.mergePolicy = NSMergePolicy(merge: NSMergePolicyType.overwriteMergePolicyType)

Work also:

managedObjectContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy