Core Data Basics

CoreDataBasics.m

    // Setting up the stack
    NSString* libraryDir = [NSSearchPathForDirectoriesInDomains(NSLibraryDirectory, NSUserDomainMask, YES) lastObject];
    NSString* storePath = [libraryDir stringByAppendingPathComponent:@"store.sqlite"];
    NSURL* storeURL = [NSURL fileURLWithPath:storePath];
    NSURL* momURL = [[NSBundle mainBundle] URLForResource:@"EmploymentModel" withExtension:@"momd"];
    NSManagedObjectModel* mom = [[NSManagedObjectModel alloc] initWithContentsOfURL:momURL];
    NSPersistentStoreCoordinator* psc = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:mom];
    
    NSDictionary* storeOptions = @{NSMigratePersistentStoresAutomaticallyOption: @YES,
                                  NSInferMappingModelAutomaticallyOption: @YES};
    NSError* error = nil;
    BOOL success = [psc addPersistentStoreWithType:NSSQLiteStoreType
                                     configuration:nil
                                               URL:storeURL
                                           options:storeOptions
                                             error:&error];
    if (!success) {
        @throw [NSException exceptionWithName:NSInvalidArgumentException
                                       reason:@"Could not initialize Core Data stack with provided parameters." userInfo:@{@"Error": error}];
    }
    
    NSManagedObjectContext* context = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
    context.persistentStoreCoordinator = psc;

    // ======================================
    // Fetching data
    NSFetchRequest* fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"MyEntity"];
    fetchRequest.predicate = [NSPredicate predicateWithFormat:@"someProperty == %@", someValue];
    
    NSSortDescriptor* sorter = [NSSortDescriptor sortDescriptorWithKey:@"someOtherProperty"
                                                             ascending:YES];
    fetchRequest.sortDescriptors = @[sorter];
    
    __block NSError* error = nil;
    __block NSArray* fetchedObjects;
    [self.moc performBlockAndWait:^{
        fetchedObjects = [self.moc executeFetchRequest:fetchRequest error:&error];
    }];
    if (fetchedObjects == nil) {
        NSLog(@"Error fetching top performing employees in department \"%@\": %@; %@",
              self.department.deptName, [error localizedDescription], [error userInfo]);
        return nil;
    }
    
    return fetchedObjects;


    // ======================================
    // Adding new objects
    MyManagedObject* object = [NSEntityDescription insertNewObjectForEntityName:@"MyEntity" inManagedObjectContext:someContext];
    // ... set the properties on object ...
    [someContext performBlock:^{
      NSError* saveError = nil;
      if (![someContext save:&saveError]) {
        NSLog(@"Failed to save: %@; %@", [saveError localizedDescription], [saveError userInfo]);
      }
    }];