Cocoa: How to avoid core-data duplicated relationships? - xcode

Question

I have these entities:
ProductsEntity
name
orders [ProductsOrderRelationship]
OrderEntity
products [ProductsOrderRelationship]
ProductsOrderRelationship
order [OrderEntity]
product [ProductsEntity]
quantity
Now, I want to edit an existing order. I have a list of products available and cart.
Now I want to add these available products to the cart.
The code must check if the products exist, so it only increases the quantity.
But, by now, it is simply adding more relationships..
Let me share a piece of code!
The interface has a list on the left with the available products and a list on the right with the cart (order entity). Both have array controllers linked to my code. Then I have this action:
- (IBAction)addSelectedProducts:(id)sender {
NSArray *firstSelectedProducts = [availableProductsController selectedObjects];
//Objects selected in the array controller
NSMutableArray *selectedProducts = [[NSMutableArray alloc] initWithCapacity:1];
//Here I will filter the repeated ones
NSMutableSet *newProducts = [NSMutableSet set];
//This is the final value to change in the current order entry.
NSMutableSet *oldProducts = [orderManagedObject valueForKey:#"products"];
//This is the old value I will change.
//Here we filter every repeated entries:
if ( [firstSelectedProducts count] > 0 ) {
for (id object in firstSelectedProducts) {
if (![oldProducts containsObject:object]) {
[selectedProducts addObject:object];
}
}
}
//Here we create objects in the relationship entity:
for (int i = 0; i < [selectedProducts count]; i++) {
// Create new relationship.
NSManagedObject *newProductObject = [
NSEntityDescription
insertNewObjectForEntityForName:#"ProductsOrderRelationship"
inManagedObjectContext:managedObjectContext
];
[newProductObject setValue:[selectedProducts objectAtIndex:i] forKey:#"product"];
[newProductObject setValue:orderManagedObject forKey:#"order"];
[newProducts addObject:newProductObject];
[newProductObject release];
}
[newProducts unionSet:oldProducts];
//Join old products and new products.
[orderManagedObject setValue:newProducts forKey:#"products"];
//Re-set the value.
//(... release stuff here)
}
I can't find a guide to this specific problem.. Any suggestions?

Answer 1

I'm guessing that firstSelectedProducts contains ProductsEntity objects and oldProducts contains ProductsOrderRelationship objects. If that's true, the problem is that...
if (![oldProducts containsObject:object]) {
...will never match anything.
(What you call ProductsOrderRelationship is often called a LineItem. Changing the name of the class and its associated variables might make the logic clearer.)