如何为我的核心数据实体建模？ [英] How to model my Core Data entity?

问题描述

我想在核心数据中存储 NoteObjects 。通常， NoteObject 具有 NSString * mainText 和 NSMutableArray * arrayOfTags （ NSStrings 的数组）。我现在想使用Core Data，但是数组对于Core Data是一件棘手的事情。通常， NoteObject 数组中的标签数量不能超过50个。那么我应该如何建模呢？我有两个选择：

I want to store NoteObjects in Core Data. Normally, a NoteObject has a NSString *mainText and an NSMutableArray *arrayOfTags (an array of NSStrings). I want to now use Core Data, but arrays are a tricky matter with core data. Typically a NoteObject won't have more than 50 tags in its array. So how should I model this? I have two options:

1. 使用 transformable 属性存储数组


2. 使用多对多关系，我读过的是更合法的方式。

1. Use a transformable property to store the array
2. Use a to-many relationship, which I've read is the more "legit" way to do it.

我应该使用哪个？为什么？以及如何使用简单的结构实现一对多关系？我似乎没办法围绕这个概念。

Which one should I use and why? And how would I implement a to-many relationship with my simple structure? I can't seem to wrap my fingers around that concept.

推荐答案

使用多对多关系。因为在获取请求期间它变得更好，更轻松。请参见下面的屏幕截图。注意右侧的关系管理器，将 NoteObject中的一对多关系设置为标记。忽略播放器实体。

Use to-many relationship. Because it's way better and easier during fetch requests. See the screenshots below. Pay attention to the Relationship manager on the right side, set "To-Many Relationship" from your NoteObject to Tags. Ignore the Player entity.

哦，请注意删除规则。您可能要删除与给定NoteObject关联的所有标签。因此，在这种情况下，请将其设置为Cascade。

Oh and pay attention to the "Delete Rule". You might want to delete all the tags associated with a given NoteObject. So set it to Cascade in that case.

NoteObject实体

NoteObject entity

标签实体

-编辑：

要添加多个标签，您需要首先获取NoteObject-I假设将使用某种ID参数来区分NoteObjects。 CoreData将自动生成标签的添加/删除方法。您将需要使用与以下代码相似的代码：

To add multiple tags you need to first fetch your NoteObject - I assume there will be some sort of ID parameter which you'll use to distinguish NoteObjects. CoreData will automatically generate the add/remove methods for Tags. You'll need to use code similar to the one below:

- (void)addTags:(NSArray *)tags toNoteObjectWithID:(NSString *)noteID {
  NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"NoteObject"];
  NSPredicate *pred = [NSPredicate predicateWithFormat:@"noteID == %@", noteID];
  [fetchRequest setPredicate:pred];
  NoteObject *noteObject = [[[self managedObjectContext] executeFetchRequest:fetchRequest error:nil] lastObject];

  for (NSString *tag in tags) {
    Tag *t = [NSEntityDescription insertNewObjectForEntityForName:@"Tag"
                                           inManagedObjectContext:[self managedObjectContext]];
    t.body = tag;
    t.noteObject = noteObject;
    [noteObject addTagsObject:t];
  }
  [self saveContext];
}

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