CODEWITHSUNDEEP
objective-ccocoacore-data
Peter Warbo
Peter Warbo

Reputation: 11710

Prevent Core Data persisting object

Is it possible to prevent Core Data to persist an object?

Let's say if I have a NSManagedObject subclass with a BOOL property isTemporary.

So when a save is called on the context I would do a check on the object:

if (self.isTemporary) {

 // Do not save

} else {

// Save this object

}

EDIT: More background information for the issue

Hmm to clarify my issue, I create an object, if it exists already I'm the db I fetch it, if it doesn't exist I insert it and set the the temporary flag of the object to YES. I set the flag because it's not clear at this stage if the user will perform a save or cancel action. If he saves I set the flag temporary to NO. If he cancels then I delete the object if temporary flag is YES.

So far so good, but in the meantime in the background there can occur core data save operations in the background that will persist these objects even though I don't want them persisted (because they should be temporary). So if I'm unlucky and app is killed I could have unwanted objects that have the temporary flag set to YES. One option would be to perform a clean operation on startup of the app to remove objects with temporary flag YES. But everything would be a whole lot easier if it would not persist those objects.

Upvotes: 1

Views: 445

Answers (2)

S1LENT WARRIOR
S1LENT WARRIOR

Reputation: 12214

If you want to prevent Core Data from persisting your ManagedObject, in other words if you don't want your object to be written in the file, you can achieve this by initializing your ManagedObject in following way:

@implementation MyManagedObject

- (id) init
{
    NSEntityDescription* entity = [NSEntityDescription entityForName:@"MyEntity" inManagedObjectContext:managedObjectContext];
    self = [super initWithEntity:entity insertIntoManagedObjectContext:Nil];
}

@end

Now if you want to save your object, save it in following way:

[managedObjectContext insertObject:myManagedObject];
NSError* error;
if ([managedObjectContext save:&error]) {
    NSLog(@"Successfully saveed ManagedObject!");                                                    
} else {
    NSLog(@"Failed to save ManagedObject!");
}

Hope this helps!

Upvotes: 0

Mundi
Mundi

Reputation: 80265

Correct, that is how it can be done. 

if (self.isTemporary && self.managedObjectContext) {
   [self.managedObjectContext delete:self];
}

Note that the managedObjectContext of a NSManagedObject becomes nil once it is deleted.

Upvotes: 1

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