Sorting array of custom objects using the value of an internal object's instance variable

Question

(sorry about the long title)

I have a custom object Person, which in turn has an NSSet which has several custom objects called Appointment. A Person therefore can have several appointments. Appointment has the values startTime and endTime.

These are Core Data NSMangagedObject classes.

@interface Person : NSManagedObject

@property (nonatomic, retain) NSString *personName;
@property (nonatomic, retain) NSSet *appointments;

// etc

@end


@interface Appointment : NSManagedObject

@property (nonatomic, retain) NSNumber * startSecond;
@property (nonatomic, retain) NSNumber * endSecond;

// etc

@end

How would I get a list of Persons, in order of the earliest startSecond within any of their appointments?

Answer 1

You can use sort descriptors and KVC collection operators:

NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"[email protected]" ascending:YES];

For example, in a CoreData fetch:

NSFetchRequest *request = [[NSFetchRequest alloc] initWithEntityName:@"Person"];

NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"[email protected]" ascending:YES];
[request setSortDescriptors:@[sortDescriptor]];

NSError *error = nil;
NSArray *sortedResults = [context executeFetchRequest:request error:&error];

Or just sorting an array:

NSArray *people = @[...];
NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"[email protected]" ascending:YES];

NSArray *sortedPeople = [people sortedArrayUsingDescriptors:@[sortDescriptor]];

More information on KVC collection operators can be found in the KVC Programming Guide.

Answer 2

If you have the data in an NSArray form you can sort it like this:

NSArray *sortedPersonArray = [coreDataPersonArray sortedArrayUsingSelector:@selector(compare:)];

- (NSComparisonResult)compare:(Person *)personObject {
    return [self.startSecond compare:personObject.startSecond];
}