CoreData：多对多关系

Question

我有 2 个对象，具有多对多关系。

这是我的代码：

+ (NSSet *)activitiesSetForMember:(Members *)member inManagedObjectContext:(NSManagedObjectContext *)context{
NSSet *activitiesSet = nil;

NSFetchRequest *request = [[NSFetchRequest alloc] init];
request.entity = [NSEntityDescription entityForName:@"CompanyActivity" inManagedObjectContext:context];
request.predicate = [NSPredicate predicateWithFormat:@"hasMembers contains %@", member];
NSError *error = nil;
activitiesSet = [[context executeFetchRequest:request error:&error] lastObject];
[request release];

NSLog(@"count: %d", [activitiesSet count]);

//se o array vem vazio (nil), não existe a o tipo de Membro
if (!error && !activitiesSet)
    NSLog(@"Error: Member has no Activities related.");

return activitiesSet;   
}

如何从选定的Member 中获取所有Activities？我怎样才能构造请求给我呢？

Answer 1

您可能已经怀疑，您的谓词有问题：

也许您因为命名关系的方式而感到困惑。这些名称似乎表明存在一些概念上的混乱。让我建议您像这样重命名您的实体和关系：

Members         - Member
CompanyActivity - Activity
memberActivity  - activities
hasMembers      - members

有一个更好的解决方案。属性活动不是已经包含您想要的活动吗？因此：

activitiesSet = member.activities; // according to my naming scheme