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PONSInvalidArgumentException: Illegal attempt to establish a relationship between objects in different contexts
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copied!<p>I have an app based on the CoreDataBooks example that uses an <code>addingManagedObjectContext</code> to add an <code>Ingredient</code> to a <code>Cocktail</code> in order to undo the entire add. The <code>CocktailsDetailViewController</code> in turn calls a <code>BrandPickerViewController</code> to (optionally) set a brand name for a given ingredient. <code>Cocktail</code>, <code>Ingredient</code> and <code>Brand</code> are all <code>NSManagedObjects</code>. <code>Cocktail</code> requires at least one <code>Ingredient</code> (<code>baseLiquor</code>) to be set, so I create it when the <code>Cocktail</code> is created.</p> <p>If I add the <code>Cocktail</code> in <code>CocktailsAddViewController : CocktailsDetailViewController</code> (merging into the Cocktail managed object context on save) without setting <code>baseLiquor.brand</code>, then it works to set the <code>Brand</code> from a picker (also stored in the Cocktails managed context) later from the <code>CocktailsDetailViewController</code>.</p> <p>However, if I try to set <code>baseLiquor.brand</code> in <code>CocktailsAddViewController</code>, I get:</p> <blockquote> <p>Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Illegal attempt to establish a relationship 'brand' between objects in different contexts'</p> </blockquote> <p>From <a href="https://stackoverflow.com/questions/1136388/passing-objects-between-managed-object-contexts">this question</a> I understand that the issue is that <code>Brand</code> is stored in the app's <code>managedObjectContext</code> and the newly added <code>Ingredient</code> and <code>Cocktail</code> are stored in <code>addingManagedObjectContext</code>, and that passing the <code>ObjectID</code> instead would avoid the crash.</p> <p>What I don't get is how to implement the picker generically so that all of the Ingredients (<code>baseLiquor</code>, <code>mixer</code>, <code>garnish</code>, etc.) can be set during the add, as well as one-by-one from the <code>CocktailsDetailViewController</code> after the <code>Cocktail</code> has been created. In other words, following the CoreDataBooks example, where and when would the <code>ObjectID</code> be turned into the <code>NSManagedObject</code> from the parent MOC in both add and edit cases? -IPD</p> <p><strong>UPDATE</strong> - Here's the add method:</p> <pre><code>- (IBAction)addCocktail:(id)sender { CocktailsAddViewController *addViewController = [[CocktailsAddViewController alloc] init]; addViewController.title = @"Add Cocktail"; addViewController.delegate = self; // Create a new managed object context for the new book -- set its persistent store coordinator to the same as that from the fetched results controller's context. NSManagedObjectContext *addingContext = [[NSManagedObjectContext alloc] init]; self.addingManagedObjectContext = addingContext; [addingContext release]; [addingManagedObjectContext setPersistentStoreCoordinator:[[fetchedResultsController managedObjectContext] persistentStoreCoordinator]]; Cocktail *newCocktail = (Cocktail *)[NSEntityDescription insertNewObjectForEntityForName:@"Cocktail" inManagedObjectContext:self.addingManagedObjectContext]; newCocktail.baseLiquor = (Ingredient *)[NSEntityDescription insertNewObjectForEntityForName:@"Ingredient" inManagedObjectContext:self.addingManagedObjectContext]; newCocktail.mixer = (Ingredient *)[NSEntityDescription insertNewObjectForEntityForName:@"Ingredient" inManagedObjectContext:self.addingManagedObjectContext]; newCocktail.volume = [NSNumber numberWithInt:0]; addViewController.cocktail = newCocktail; UINavigationController *navController = [[UINavigationController alloc] initWithRootViewController:addViewController]; [self.navigationController presentModalViewController:navController animated:YES]; [addViewController release]; [navController release]; } </code></pre> <p>and here's the site of the crash in the <code>Brand</code> picker (this <code>NSFetchedResultsController</code> is backed by the app delegate's managed object context:</p> <pre><code>- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath { UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath]; cell.accessoryType = UITableViewCellAccessoryCheckmark; if ([delegate respondsToSelector:@selector(pickerViewController:didFinishWithBrand:forKeyPath:)]) { [delegate pickerViewController:self didFinishWithBrand:(Brand *)[fetchedResultsController objectAtIndexPath:indexPath] forKeyPath:keyPath]; // 'keyPath' is @"baseLiquor.brand" in the crash } } </code></pre> <p>and finally the delegate implementation:</p> <pre><code>- (void)pickerViewController:(IngredientsPickerViewController *)pickerViewController didFinishWithBrand:(Brand *)baseEntity forKeyPath:(NSString *)keyPath { // set entity [cocktail setValue:ingredient forKeyPath:keyPath]; // Save the changes. NSError *error; if (![cocktail.managedObjectContext save:&error]) { // Update to handle the error appropriately. NSLog(@"Unresolved error %@, %@", error, [error userInfo]); exit(-1); // Fail } // dismiss picker [self.navigationController popViewControllerAnimated:YES] } </code></pre> <p><strong>EVEN MORE</strong></p> <p>I'm making progess based on Marcus' suggestions -- I mapped the <code>addingManagedObjectContexts</code> to the parent managedObjectContext and wrapped everything in <code>begin/endUndoGrouping</code> to handle cancel vs. save. </p> <p>However, the object to be created is in an <code>NSFetchedResultsController</code>, so when the user hits the "+" button to add the <code>Cocktail</code>, the (possibly-to-be-undone) entity briefly appears in the table view as the modal add view controller is presented. The MDN example is Mac-based so it doesn't touch on this UI behavior. What can I do to avoid this?</p>

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