Adding attribute value to core data IF value already exists

Question

I have to say that everyone on the forum has been really helpful with my attempts at learning core data.

I am adding attribute values to my core data entities and creating a relationship when the user selects a row as shown below:

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath*)indexPath
{

UIAlertView *messageAlert = [[UIAlertView alloc]
                                 initWithTitle:@"Row Selected" message:@"Added to Routine!" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];

    NSManagedObjectContext *context = [self managedObjectContext];

    // Create a new device
    ExcerciseInfo *info = [_fetchedResultsController objectAtIndexPath:indexPath];
NSManagedObject *routineEntity = [NSEntityDescription insertNewObjectForEntityForName:@"Routines"inManagedObjectContext:context];
NSManagedObject *routineEntityDetail = [NSEntityDescription insertNewObjectForEntityForName:@"RoutinesDetails" inManagedObjectContext:context];

[routineEntityDetail setValue:routineEntity forKey:@"routineinfo"];

    [routineEntity setValue: RoutineText  forKey:@"routinename"];
    [routineEntityDetail setValue: info.details.muscle  forKey:@"image"];

How would I include an IF statement whereby if the routinename already exists the new entry would be added to the existing relationship?

Is this easily possible from the current code? So the Test Routines will be grouped instead of showing separately and the detail view would include both entries. Would NSPredicatebe appropriate here? Or perhaps the use of distinctUnionOfObjects?

You thoughts and comments will be appreciated.

AS REQUESTED -

- (NSFetchedResultsController *)fetchedResultsController {

    if (_fetchedResultsController != nil) {
        return _fetchedResultsController;
    }

    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription
                                   entityForName:@"Routines" inManagedObjectContext:managedObjectContext];
    [fetchRequest setEntity:entity];

    NSSortDescriptor *sort = [[NSSortDescriptor alloc]
    initWithKey:@"routinename" ascending:NO];
    [fetchRequest setSortDescriptors:[NSArray arrayWithObject:sort]];

    [fetchRequest setFetchBatchSize:20];

    NSFetchedResultsController *theFetchedResultsController =
    [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
                                        managedObjectContext:managedObjectContext sectionNameKeyPath:nil
                                                   cacheName: nil];
    self.fetchedResultsController = theFetchedResultsController;
    _fetchedResultsController.delegate = self;

    return _fetchedResultsController;

Answer 1

You don't need to care about this, you can simply insert a new RoutineDetails object and Core Data takes care of the rest. When you auto-generate the NSManagedObjectsubclasses of your DB tables, Core Data automatically generates accessor methods for all relationships, where you can add and remove single or multiple instances of RoutineDetails from Routines.

To create NSManagedObject subclasses, go to your ManagedObjectModel click on Editor->Create NSManagedObject subclass… and create subclasses for your entities:

In your new subclass, you'll see methods like:

@interface Routines (CoreDataGeneratedAccessors)
- (void)addRoutineDetailsObject:(RoutineDetails *)value;
- (void)removeRoutineDetailsObject:(RoutineDetails *)value;
- (void)addRoutineDetails:(NSSet *)values;
- (void)removeRoutineDetails:(NSSet *)values;

Than you can access all the RoutineDetails directly through the Routines object (you'll get an NSSet of RoutineDetails), and furthermore you can add new objects with

[routineEntity addRoutineDetailsObject:routineEntityDetail];

not caring if an object already exists or not. Core Data will do the right thing.

Comment regarding Core Data: Core Data can have a lot boilerplate code for simple things like fetching. Take a look at the MagicalRecord project, which is much less verbose and does wonders.

EDIT: Whenever you previously created NSManagedObject, now you can directly use your own classes, i.e. Routines. That way you'll have access to all the "new functionality".