Hello,
Supposing you had a Core Data relationship such as:
Book ---->> Chapter ---->> Page
Given a Book object called aBook, aBook.chapters will return the book's chapters. But how do you get a book's pages (i.e. book.pages)? And how would you get the pages sorted by a pageNumber property?
Thank you!
Given a Book instance, myBook:
NSSet* pages = [myBook valueForKeyPath:@"[email protected]"];
will give you the union of all pages. See the "Set and Array Operators" section in the Key-Value Coding Programming guide.
NSArray *chaperPages = [myBook.chapters valueForKeyPath:@"pages"];
will give you an array of NSSets of pages, one set per chapter.
@Barry -- so those will span Core Data relationships? Where is this all explained in a coherent way?
The quickest way to get all Pages of a Book (myBook) sorted by pageNumber would be:
NSSet *pageSet = [myBook valueForKey:@"[email protected]"];
NSSortDescriptor *sortDesc = [[NSSortDescriptor alloc] initWithKey@"pageNumber" ascending:YES];
NSArray *pages = [pageSet sortedArrayUsingDescriptors:[NSArray arrayWithObject:sortDesc]];
[sortDesc release];
This will yield an array with all pages from all chapters sorted by pageNumber