Question

How to obtain an ordered list of coredata managed objects via accessing them via a relationship?

That is:

• have the following entities: LIST, LIST_ITEM (includes an ‘Order’ field), and ITEM.
• assume that I have already fetched the list I want to work with
• I can then use the coredata relationships to get the LIST_ITEMS via using the relationship: e.g. “list1.listItems”, and then for each of these LIST_ITEMS I can get the ITEM (“listItem1.item”)

But if I really just want, from the LIST, an ordered list of ITEMS from the list, based on the “Order” field in the LIST_ITEM, what is the easiest way of doing this?

Answer 1

You can sort the items returned by the relationship using an NSSortDescriptor just as you would in a regular fetch request. For example:

NSSortDescriptor *sortDescriptor = [[[NSSortDescriptor alloc] initWithKey:@"order" ascending:YES] autorelease];
NSArray *sortedListItems =  [list1.listItems sortedArrayUsingDescriptors:[NSArray arrayWithObject:sortDescriptor]];

The key method here is [NSSet sortedArrayUsingDescriptors:]