Deleting Specific Object From Core Data (Swift)

Question

In my Core Data Entity Favorite , I am appending Strings to its Attribute fav .

When I look up a fav object based on String name and try to it, it is not deleting the entry, but instead is setting that object's fav = nil 时，它不是删除条目，而是设置该对象的fav = nil

Here is my code:

let managedContext = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext!
let favoriteFetchRequest = NSFetchRequest(entityName:"Favorite")

let predicate = NSPredicate(format: "fav == %@", "snowboarding")

   favoriteFetchRequest.predicate = predicate

let fetchedEntities = managedContext.executeFetchRequest(favoriteFetchRequest, error: nil) as! [NSManagedObject]

    for entity in fetchedEntities {
       managedContext.deleteObject(entity)

       if !managedContext.save(&error) {
          println("Could not save \(error)")
       }
    }

When I rerun the app and have all Entity data display, the log shows:

<NSManagedObject: 0x7fc8b0d1e4f0> (entity: Favorite; id: 0xd000000000080000 <x-coredata://8984EF48-71AF-4B87-AA59-EE5999038369/Favorite/p2> ; data: {
fav = nil;})

This is turn creates a whole bunch of nil entries and the Core Data is never empty (as I'd like it to be at times). What am I doing wrong? How do I delete the entire object?

Answer 1

Whenever I do anything with CoreData , I take care of all the transactions before saving. Adding new Entities , saving new Entity attributes, etc. (Well, I shouldn't say all , but in most cases when I'm doing an update)

I'm not sure if this will fix it but try moving your

if !managedContext.save(&error) {
    println("Could not save \(error)")
}

Out of the for loop and instead have it read:

for entity in fetchedEntities {
    managedContext.deleteObject(entity)
}
if !managedContext.save(&error) {
    println("Could not save \(error)")
}

The rest of the code looks fine so this is the only thing I can blatantly see that differs from how I usually update my CoreData entries. Let me know if that solves anything.

EDIT: A little bug investigation you could as well is after the for loop, access the managedContext 's deletedObjects property and check the count of that NSSet and see if it is actually registering those objects to be deleted.