core-data - 如何提取核心数据中的数据关系？

Question

我有两个实体：人员和网络（xcdatamodeld 屏幕 - http://rghost.ru/47818182/image.png）。在方法fetch我提取数组 peoples 并且我想打印network.url。

错误：

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[_NSFaultingMutableSet url]: unrecognized selecto

代码：

    - (IBAction)insert:(id)sender
{
    NSMutableSet* networks = [NSMutableSet set];

    // People entity
    People *people = (People *)[NSEntityDescription insertNewObjectForEntityForName:@"People" inManagedObjectContext:self.managedObjectContext];
    people.name = @"Alex";
    people.age = @23;

    // Network entity
    Network *network = (Network *)[NSEntityDescription insertNewObjectForEntityForName:@"Network" inManagedObjectContext:self.managedObjectContext];
    network.url = @"http://facebook.com/alex";
    [networks addObject:network];
[people addNetwork:networks];

    // Save
    [self.managedObjectContext save:nil];
}

- (IBAction)fetch:(id)sender
{
    NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"People"];
    NSArray *peoples = [self.managedObjectContext executeFetchRequest:fetchRequest error:nil];

    for (People *people in peoples)
    {
        Network *network = (Network *)people.network;
        NSLog(@"%@", network.url);
    }
}

Answer 1

“People ->> Network”是一对多关系，因此people.network 是一组Network 对象，而不是单个 Network 对象。以下应该有效：

for (People *people in peoples)
{
    for (Network *network in people.network)
    {
        NSLog(@"%@", network.url);
    }
}

Answer 2

因为人与网络之间的关系太多了。所以如果你查看你的ManagedObject类，你的对象将返回 NSSet People。所以你的循环应该是这样的。

for (People *people in [peoples allObjects])
{
    Network *network = (Network *)people.network;
    NSLog(@"%@", network.url);
}