Core Data addObject 一对多关系

Question

我尝试将对象添加到我的核心数据模型中。但是，当我尝试显示它们时，它们并不存在。我正在使用类别作为助手。

+ (Project *)createProjectWithDictionary:(NSDictionary *)dic inManagedObjectContext:(NSManagedObjectContext *)managedObjectContext {

    Project *project = nil;

    // Build a fetch request to see if we can find this Flickr photo in the database.
    // The "unique" attribute in Photo is Flickr's "id" which is guaranteed by Flickr to be unique.

    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Project"];
    request.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"title" ascending:YES]];
    request.predicate = [NSPredicate predicateWithFormat:@"title = %@", [dic[kTagProjectTitle]description]];

    // Execute the fetch

    NSError *error = nil;
    NSArray *matches = [managedObjectContext executeFetchRequest:request error:&error];

    // Check what happened in the fetch

    if (!matches || ([matches count] > 1)) {  // nil means fetch failed; more than one impossible (unique!)
        // handle error
    } else if (![matches count]) { // none found, so let's create a Photo for that Flickr photo
        project = [NSEntityDescription insertNewObjectForEntityForName:@"Project" inManagedObjectContext:managedObjectContext];
        NSLog(@"Encontrado Primera vez");

        project.projectId = [NSNumber numberWithInt:[[dic valueForKey:kTagProjectId] intValue]];
        project.title = [dic valueForKey:kTagProjectTitle];
        project.estimatedPrice = [NSNumber numberWithInt:[[dic valueForKey:kTagProjectEstimatedPrice] floatValue]];
        NSMutableArray *tags = [[NSMutableArray alloc] init];
        tags = [dic objectForKey:kTagProjectsTags];

        NSMutableSet *tagSet = [[NSMutableSet alloc]init];
        for (NSDictionary * tagDic in tags){
            NSString *tagName = [tagDic objectForKey:kTagProjectTagName];
            Tag *tag = [Tag insertTagName:tagName inManagedObjectContext:managedObjectContext];
            [project addTagsObject:tag];
        }

       // [project addTags:tagSet];

我尝试过使用带有 addObject:(NSSet *tag) 的 NSMutableSet 以及 addTagObject 并且我在 NSLog 中有相同的输出。

            for( Tag *tag in project.tags){
                NSLog(@"TAG TITLES %@", tag.name);  
            }
       2013-09-30 23:03:36.003 Prototype[28959:c07] TAG TITLES iOS
       2013-09-30 23:03:36.004 Prototype[28959:c07] TAG TITLES Windows Phone
    }

然后，当我尝试在单元格中显示它们时。我有一个新的 NSLog，这是输出。为什么在第一个 NSLog 中我可以看到它们，而不是在 cellForRowAtIndexPath 方法中？

- (UITableViewCell *)tableView:(UITableView *)aTableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
   Project *project = (Project *)[self.data objectAtIndex:indexPath.row];
   NSLog(@"TITLE %@", project.tags);
}

输出

 TITLE Relationship 'tags' on managed object (0x7c60ba0) <Project: 0x7c60ba0> (entity: Project; id: 0x7c60be0 <x-coredata:///Project/tE9F74F99-04BC-43CC-BD68-F435712B3B3C9> ; data: {

    estimatedPrice = 1999;
    projectId = 418;
    tags =     (
    );
    title = "Aplicaci\U00f3n IOS";
    "yp_desc" = nil;
}) with objects {(
)}

}

Answer 1

很可能您在添加标签后没有保存上下文。

Answer 2

我建议你使用 Magical Record 框架 (https://github.com/magicalpanda/magicalrecord)，它让 Core Data 管理变得更加容易！

另一方面，如果你想继续没有它，我会尝试改变：

 + (Project *)createProjectWithDictionary:(NSDictionary *)dic inManagedObjectContext:(NSManagedObjectContext *)managedObjectContext {

    Project *project = nil;

    // Build a fetch request to see if we can find this Flickr photo in the database.
    // The "unique" attribute in Photo is Flickr's "id" which is guaranteed by Flickr to be unique.

    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Project"];
    request.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"title" ascending:YES]];
    request.predicate = [NSPredicate predicateWithFormat:@"title = %@", [dic[kTagProjectTitle]description]];

    // Execute the fetch

    NSError *error = nil;
    NSArray *matches = [managedObjectContext executeFetchRequest:request error:&error];

    // Check what happened in the fetch

    if (!matches || ([matches count] > 1)) {  // nil means fetch failed; more than one impossible (unique!)
        // handle error
    } else if (![matches count]) { // none found, so let's create a Photo for that Flickr photo
        project = [matches lastObject];
        NSLog(@"Encontrado Primera vez");

        //Makes that only if you want to rehydrate your saved object. At other way I am not sure what yo want to do here :S
        project.projectId = [NSNumber numberWithInt:[[dic valueForKey:kTagProjectId] intValue]];
        project.title = [dic valueForKey:kTagProjectTitle];
        project.estimatedPrice = [NSNumber numberWithInt:[[dic valueForKey:kTagProjectEstimatedPrice] floatValue]];
        NSMutableArray *tags = [[NSMutableArray alloc] init];
        tags = [dic objectForKey:kTagProjectsTags];

        for (NSDictionary * tagDic in tags){
            NSString *tagName = [tagDic objectForKey:kTagProjectTagName];
            Tag *tag = [NSEntityDescription insertNewObjectForEntityForName:@"Tag" inManagedObjectContext:managedObjectContext];
            //TODO: populate tag object using tagDic
            [project addTagsObject:tag];
        }

如果您尚未保存当前上下文，请记住在同一上下文中进行提取；)