iOS 6 Programming Cookbook

15.6. Sorting Data in Core Data

Problem

You want to sort the managed objects (records) that you fetch from a managed object context (database).

Solution

Create instances of NSSortDescriptor for each attribute (column, in the database world) of an entity that has to be sorted. Add the sort descriptors to an array and assign the array to an instance of NSFetchRequest using the setSortDescriptors: instance method. In this example code, Sorting_Data_in_Core_DataAppDelegate is the class that represents the app delegate in a universal app. To understand how the Person entity is created, please refer to Recipes 15.1 and 15.2:

- (BOOL)            application:(UIApplication *)application
  didFinishLaunchingWithOptions:(NSDictionary *)launchOptions{

  [self createNewPersonWithFirstName:@"Richard"
                            lastName:@"Branson"
                                 age:61];

  [self createNewPersonWithFirstName:@"Anthony"
                            lastName:@"Robbins"
                                 age:51];

  /* Create the fetch request first */
  NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];

  /* Here is the entity whose contents we want to read */
  NSEntityDescription *entity =
  [NSEntityDescription entityForName:@"Person"
              inManagedObjectContext:self.managedObjectContext];  
  NSSortDescriptor *ageSort =
  [[NSSortDescriptor alloc] initWithKey:@"age"
                              ascending:YES];

  NSSortDescriptor *firstNameSort =
  [[NSSortDescriptor alloc] initWithKey:@"firstName"
                              ascending:YES];

  NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:
                              ageSort,
                              firstNameSort, nil];

  fetchRequest.sortDescriptors = sortDescriptors;

  /* Tell the ...