按属性排序NSManagedObjects的NSSet

Question

如果NSSet包含的对象是一个NSManagedObject带有字符串属性的子类name,则如何按名称对该集进行排序？这是我要用的地方NSPredicate吗？

谢谢!

Answer 1

不,但你会用NSSortDescriptor.

你可以使用这样的sortedArrayUsingDescriptors:方法:

NSSortDescriptor *nameDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES];
NSArray *sorted = [yourSet sortedArrayUsingDescriptors:[NSArray arrayWithObject:nameDescriptor]];

Answer 2

通过提及NSPredicate,我觉得OP想要将集合排序为执行获取的一部分.无论他是否意味着这一点,这都是一个例子.假设您在Employee实体和Department实体之间存在多对多关系,即部门包含许多员工.鉴于您已经获取了部门,请获取部门中的员工并按名字对其进行排序:

使用MagicalRecord:

Department *department = someFetchedDepartment; 
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"department == %@", department];
NSArray *sortedEmployees = [Employee MR_findAllSortedBy:@"firstName" ascending:YES withPredicate:predicate];

没有MagicalRecord:

NSFetchRequest *request = [[NSFetchRequest alloc] init];    

NSEntityDescription *employeeEntity = [NSEntityDescription @"Employee" inManagedObjectContext:self.context];
[request setEntity:employeeEntity];

Department *department = someFetchedDepartment; 
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"department == %@", department];
[request setPredicate:predicate];

NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"firstName" ascending:ascending];
[request setSortDescriptors:@[sortDescriptor]];

NSError *error = nil;
NSArray *sortedEmployees = [self.context executeFetchRequest:request error:&error];