Sort NSArray with multiple predicates in Objective C

Question

I have an array that contains some core data objects. Each object has three attributes say "First Name" & "Last Name"

I want to filter & sort the array as per the search letter(s). The final list should be in this order:

Records that starts with first name as like searched text should come first
Records that starts with last name as like searched text should come second
Records that contains first name as like searched text should come third
Records that contains last name as like searched text should come fourth

I confused in creating predicates and sort descriptors. Can anyone help?

Edit:

Here is my fetched results controller:

-(NSFetchedResultsController *)myFetchedResultsController
{
    if (!_myFetchedResultsController)
    {
        ...
        ...

        NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:MY_ENTITY_NAME];

        NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(firstName beginswith[cd] %@) || (lastName beginswith[cd] %@) || (firstName contains[cd] %@) || (lastName contains[cd] %@))", self.searchText, self.searchText, self.searchText, self.searchText];

        [fetchRequest setPredicate:predicate];


        //I really dont have idea about how to set sort description to this scenario

        NSSortDescriptor *firstNameDescriptors = [[NSSortDescriptor alloc] initWithKey:@"firstName" ascending:YES selector:@selector(localizedCaseInsensitiveCompare:)];
        NSSortDescriptor *lastNameDescriptors = [[NSSortDescriptor alloc] initWithKey:@"lastName" ascending:YES selector:@selector(localizedCaseInsensitiveCompare:)];

        [fetchRequest setSortDescriptors:@[firstNameDescriptors, lastNameDescriptors]];

        _userFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:appDelegate.managedObjectContext sectionNameKeyPath:nil cacheName:nil];
    }

    return _myFetchedResultsController;
}

But this seems not working, means it does not sort the objects.

could you please show what you have tried and where you are facing the issue ? — Teja Nandamuri
– Teja Nandamuri, Commented May 5, 2016 at 12:48

Community · Accepted Answer · 2017-05-23 12:31:41Z

But this seems not working, means it does not sort the objects.

Do you really mean it does not sort, or that it does not sort they way you wish?

NSSortDescriptor takes a single key on which to sort. In a situation where you have a primary key and a secondary key where you sort using the secondary key only if the primary keys are equal, e.g. family name then given name, then routines such as the setSortDescriptors: exist which take an array of sort descriptors. This is the kind of sort you have setup in your code.

However this is not the kind of sort you have specified in your bullets. Your sort requires access to multiple keys to determine the order - it says of the first key meets a particular condition then sort on that key, else if the second key meets a particular condition then sort on that key, etc. To perform this kind of sort you can write an NSComparator block which has access to the complete objects - not just the values of a particular key - and implement your algorithm as a combination of tests and comparisons.

Unfortunately for you this second kind of sort is not supported directly by NSFetchRequest. Instead you will need to obtain the results without sorting and then sort the resultant array with a method such as sortedArrayUsingComparator:.

For a related question see NSSortDescriptor: Custom comparison on multiple keys simultaneously.

HTH

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