SELF, self in CORE DATA

Predicate

SELF

Represents the object being evaluated.

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CORE DATA

Retrieving Specific Objects

If your application uses multiple contexts and you want to test whether an object has been deleted from a persistent store, you can create a fetch request with a predicate of the form self == %@. The object you pass in as the variable can be either a managed object or a managed object ID, as in the following example:

NSFetchRequest *request = [[NSFetchRequest alloc] init];

NSEntityDescription *entity =

[NSEntityDescription entityForName:@"Employee"

inManagedObjectContext:managedObjectContext];

[request setEntity:entity];

NSPredicate *predicate =

[NSPredicate predicateWithFormat:@"self == %@", targetObject];

[request setPredicate:predicate];

NSError *error;

NSArray *array = [managedObjectContext executeFetchRequest:request error:&error];

if (array != nil) {

NSUInteger count = [array count]; // May be 0 if the object has been deleted.

//

}

else {

// Deal with error.

}

The count of the array returned from the fetch will be 0 if the target object has been deleted. If you need to test for the existence of several objects, it is more efficient to use the IN operator than it is to execute multiple fetches for individual objects, for example:

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"self IN %@",

arrayOfManagedObjectIDs];