Core Data saving problem: can't update transformable attribute (NSArray)

Question

I have a strange problem in my Core Data app.

I have three entities in my app, but today I found a problem with one of them. My problematic entity is called Invoice and it has many attributes, including Products. It's encoded NSArray of NSDictionaries (via default NSValueTransformer).

Everything works fine - i create my invoice, its client, its products, etc. Everything works.

But, when I choose my invoice from a list and then try to edit its products and click 'Save' button, my save works only until my app gets terminated.

The problem is only with my products array - the rest (e.g. payment date, client etc.) saves.

---

What am I doing

I pass my Invoice object via

NSManagedObject *inv = [self.fetchedResultsController objectAtIndexPath:indexPath];
invoiceEditor.invoice = inv;

And save my data (in my InvoiceEditor VC):

[self.invoice setValue:client forKey:@"Client"] // NSDictionary;
[self.invoice setValue:products forKey:@"Products"] // NSArray of NSDictionaries;
[self.invoice setValue:pmDate forKey:@"PaymentDate"] // NSDate;
// other attributes
NSManagedObjectContext *context = self.invoice.managedObjectContext;
NSError *error = nil;
if (![context save:&error]) {
    NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
    abort();
}

Everythings saves until being terminated: client, products, dates. But only products are 'reseted' after termination.

Anybody?

Answer 1

Just found the problem. From Model Object Implementation Guide:

If there are mutable and immutable versions of a class you use to represent a property—such as NSArray and NSMutableArray—you should typically declare the return value of the get accessor as an immutable object even if internally the model uses a mutable object.

And my products array was actually a NSMutableArray instance. I solved it by copying products (so I converted mutable array to immutable array). Now it works. :) And I didn't need to start the bounty...