Question

我在以下关系中设置了两个对象：

新闻＆lt; - ＆gt;＆gt;链路

链接包含两个属性，其中一个是URL，另一个是关联文本。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循环中，我创建一个Link：

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];

完成for循环后，我将我创建的Link集创建为News对象：

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

当我获取数据时，我可以获取新闻的信息，但是当我获取链接时，我什么也得不回来：

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"]];
    }

当我尝试访问我的相关对象时，有人可以告诉我为什么我会找回0个对象吗？

Answer 1

为什么不使用

NSSet *setOfLinks = newsObject.links;

Answer 2

我用以下代码解决了它：

NSEntityDescription *linkEntity = [NSEntityDescription entityForName:@"Link"inManagedObjectContext:context]; 
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"ANY id == %@", [info valueForKey:@"id"]]; 
[fetchRequest setEntity:linkEntity]; 
[fetchRequest setPredicate:predicate]; 
NSArray *results = [context executeFetchRequest:fetchRequest error:&error];

Fetch不会从一对多关系对象返回任何内容

2 个答案: