NSSortDescriptor sorting with part of key possible?

Question

I have a CoreData iphone application with a view that display addresses.

An address looks like this: "5 Blob Street, 2222, Suburbia", where "5 Blob Street" is the address_and_number key, "2222" the post code, and "Suburbia" the suburb.

Currently I use this NSSortDescriptor, which works fine:

NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] 
                                    initWithKey:@"address_and_number" ascending:YES];

However, my client wants to sort by street name, i.e. out of the address_and_number key, "Blob Street" would be evaluated.

Is there any way to do such sorting without resorting to splitting the address_and_number key into two keys, "address" and "number"?

Can I use perhaps a regular expression to grab only the part of the address_and_number key I need for sorting, and somehow add that to the NSSortDescriptor object?

Answer 1

Try adding a NSComparator block to the initialization of the NSSortDescriptor like this:

    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc]
                                    initWithKey:@"Address_suburb" ascending:YES comparator:^NSComparisonResult(id obj1, id obj2) {
                                      // do your comparison without house numbers here
                                      // return either NSOrderedAscending, NSOrderedDescending or NSOrderedSame
                                    }];

Answer 2

According to the answer at a relevant question at Custom sorting using categories and core data - is it supported by the framework?

Sorting inside of the NSFetchedResultsController is performed at the persistent store level so if you are using SQLite as the backend it will fail.

For something like this I would de-normalize the data and store the month and day of month in addition to the actual birthdate so that you can sort on them.

After trying both a selector and a comparator, none of which worked as my persistent level I am using sqlite3, I resorted to splitting the address_and_number key into address_street_name and address_street_number keys, and then sorting by address_street_name.