ios - Fetch 从一对多关系对象中不返回任何内容

Question

我有两个对象设置为以下关系:

新闻<->>链接

Link 包含两个属性，其中一个是 URL，另一个是一些关联文本。我最初创建了新闻并用信息填充它:

NSManagedObject *newsData = [NSEntityDescription
                                         insertNewObjectForEntityForName:@"News"
                                         inManagedObjectContext:context];
        [newsData setValue:[object objectForKey:@"username"] forKey:@"username"];
        [newsData setValue:message forKey:@"content"];
        [newsData setValue:[object objectForKey:@"when"] forKey:@"date"];
        [newsData setValue:imgUrl forKey:@"img"];

        NSMutableSet *links = [launchTicker mutableSetValueForKey:@"links"];

然后在 for 循环内，我创建一个链接:

NSManagedObject *linkInfo = [NSEntityDescription
                                                          insertNewObjectForEntityForName:@"Link"
                                                          inManagedObjectContext:context];
                    [linkInfo setValue:[object objectForKey:@"id"] forKey:@"id"];
                    [linkInfo setValue:[[item firstChild] content] forKey:@"text"];
                    [linkInfo setValue:[[item attributes] valueForKey:@"href"] forKey:@"url"];
                    [links addObject:linkInfo];

for循环完成后，我将我创建的Link集合放入News对象中:

[newsData setValue:links forKey:@"links"];

当我获取数据时，我可以很好地获取新闻信息，但是当我获取链接时，我什么也没有得到:

for (NSManagedObject *info in fetchedObjects) {

    [fetchRequest setReturnsObjectsAsFaults:NO];
    [fetchRequest setRelationshipKeyPathsForPrefetching:[NSArray arrayWithObjects:@"links", nil]];

    NSMutableArray *url = [[NSMutableArray alloc] init];
    NSMutableArray *text = [[NSMutableArray alloc] init];

    NSSet* links = [info valueForKey:@"links"];
    NSArray *arrayLinks = [links allObjects];

    for(NSManagedObject *link in arrayLinks) {
        [url addObject:[link valueForKeyPath:@"url"]];
        [text addObject:[link valueForKeyPath:@"text"]];
    }

任何人都可以深入了解为什么我在尝试访问相关对象时返回 0 个对象吗？

Answer 1

为什么不直接使用

NSSet *setOfLinks = newsObject.links;