Iterate through NSManagedObjectContext objects?

Question

I want to iterate through all of the objects in my NSManagedObjectContext, and update them manually. Then, every managed object should be updated. What's the best way to do this?

Answer 1

Theoretically you could iterate through all the entity descriptions in your managed object model, build a no-predicate fetch request for them, then loop over all the returned objects and do some update. Example:

// Given some NSManagedObjectContext *context
NSManagedObjectModel *model = [[context persistentStoreCoordinator]
                               managedObjectModel];
for(NSEntityDescription *entity in [model entities]) {
    NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];
    [request setEntity:entity];
    NSError *error;
    NSArray *results = [context executeFetchRequest:request error:&error];
    // Error-checking here...
    for(NSManagedObject *object in results) {
        // Do your updates here
    }
}

Note you can cast the NSManagedObjects returned as necessary either by testing for class equality (using isKindOfClass: or a related method) or by figuring out what class the current entity is (using the managedObjectClassName property on entity in conjunction with the NSClassWithName() method).

Answer 2

This seems like a very heavy handed approach to the problem. If the data is getting loaded with bad data then i would strongly suggest fixing it while you are importing the data. Tim's answer will work for what you are doing but I strongly suspect you are coming at this wrong. Iterrating through the whole database looking for potentially bad data is very inefficient.