How to store array of NSManagedObjects in an NSManagedObject
- by David Tay
I am loading my app with a property list of data from a web site. This property list file contains an NSArray of NSDictionaries which itself contains an NSArray of NSDictionaries. Basically, I'm trying to load a tableView of restaurant menu categories each of which contains menu items.
My property list file is fine. I am able to load the file and loop through the nodes structure creating NSEntityDescriptions and am able to save to Core Data. Everything works fine and expectedly except that in my menu category managed object, I have an NSArray of menu items for that category. Later on, when I fetch the categories, the pointers to the menu items in a category is lost and I get all the menu items. Am I suppose to be using predicates or does Core Data keep track of my object graph for me?
Can anyone look at how I am loading Core Data and point out the flaw in my logic? I'm pretty good with either SQL and OOP by themselves, but am a little bewildered by ORM. I thought that I should just be able to use aggregation in my managed objects and that the framework would keep track of the pointers for me, but apparently not.
NSError *error;
NSURL *url = [NSURL URLWithString:@"http://foo.com"];
NSArray *categories = [[NSArray alloc] initWithContentsOfURL:url];
NSMutableArray *menuCategories = [[NSMutableArray alloc] init];
for (int i=0; i<[categories count]; i++){
MenuCategory *menuCategory = [NSEntityDescription
insertNewObjectForEntityForName:@"MenuCategory"
inManagedObjectContext:[self managedObjectContext]];
NSDictionary *category = [categories objectAtIndex:i];
menuCategory.name = [category objectForKey:@"name"];
NSArray *items = [category objectForKey:@"items"];
NSMutableArray *menuItems = [[NSMutableArray alloc] init];
for (int j=0; j<[items count]; j++){
MenuItem *menuItem = [NSEntityDescription
insertNewObjectForEntityForName:@"MenuItem"
inManagedObjectContext:[self managedObjectContext]];
NSDictionary *item = [items objectAtIndex:j];
menuItem.name = [item objectForKey:@"name"];
menuItem.price = [item objectForKey:@"price"];
menuItem.image = [item objectForKey:@"image"];
menuItem.details = [item objectForKey:@"details"];
[menuItems addObject:menuItem];
}
[menuCategory setValue:menuItems forKey:@"menuItems"];
[menuCategories addObject:menuCategory];
[menuItems release];
}
if (![[self managedObjectContext] save:&error]) {
NSLog(@"An error occurred: %@", [error localizedDescription]);
}
