Removing a binary attribute's data(used in NSImageView) in Core Data entity

Question

Hello guys,

I have an optional binary attribute: image , containing an image for my entities. In the interface, I have NSImageView (Image Well), and a "Remove Image" button. When the image removing button is clicked, I do:

- (IBAction)saveAction:(id)sender {
  NSError *error = nil;
  if (![[self managedObjectContext] save:&error]) {
    [[NSApplication sharedApplication] presentError:error];
  }
  [tableView reloadData];
}

- (IBAction)removeImage:(id)sender {
  [image setImage:nil]; // image is a NSImageView outlet bound to the image attribute.
  [self saveAction:sender];
}

It clears the image from the NSImageView, but the binary data is still retained in the Core Data entity.

How do I reflect the change in the Core Data entity as well?

Thanks!

Edit:

NSImageView is already bound to model's image attribute, and available as outlet too. So I'm just looking for someone to tell me how to reset the attribute by fetching the model (if that's what I need to do).

Would appreciate any code help. :)

Answer 1

[image setImage:nil];

Is image actually an image view? If so, I must remind you to name your instance variables clearly and accurately.

You need to set the image property of the model object(s), not the view(s). Bind the views through the controllers to the model; then, when you change the model, the views pick up the changes for free.

Answer 2

I was under impression that altering an array from a fetch request won't make a difference to the actual data in storage. But I was wrong. I tried and it worked! Thanks Peter, and everyone elsewhere!

Here's what I replaced my image removal function for currently selected entity having a unique attribute:

- (IBAction)removeImage:(id)sender {
  // Fetch the entity in question.
  NSManagedObjectContext *context = [self managedObjectContext];
  NSManagedObjectModel *model = [self managedObjectModel];
  NSEntityDescription *entity = [[model entitiesByName] valueForKey:@"myEntity"];
  NSPredicate *predicate = [NSPredicate predicateWithFormat:
                            @"unique_attr == %@", [unique_attr_outlet stringValue]];
  NSFetchRequest *fetch = [[NSFetchRequest alloc] init];
  [fetch setEntity:entity];
  [fetch setPredicate:predicate];

  // Load it into NSArray object and remove the binary data attribute.
  NSArray *contextArray = [context executeFetchRequest:fetch error:nil];
  if ([contextArray count] > 0)
    [[contextArray objectAtIndex:0] setValue:nil forKey:@"myImage"];

  [fetch release];
}