iOS Core Data - 将相关数据添加到实体

Question

这里是 iOS 初学者。

给定一个具有多对多关系的实体

@class Categories;

@interface Events : NSManagedObject

@property (nonatomic, retain) NSString * title;
@property (nonatomic, retain) NSSet *categories;
@end

@interface Events (CoreDataGeneratedAccessors)

- (void)addCategoriesObject:(Categories *)value;
- (void)removeCategoriesObject:(Categories *)value;
- (void)addCategories:(NSSet *)values;
- (void)removeCategories:(NSSet *)values;

@end

相关

@interface Categories : NSManagedObject

@property (nonatomic, retain) NSString * name;
@property (nonatomic, retain) NSManagedObject *events;

@end

并且有一些 JSON 数据来填充事件表

[{"title": "Test Exhibition", "categories": [{"name": "Exhibitions"}]}, {...}]

我应该如何格式化 JSON 数据以执行类似的操作

// Parse Events JSON
[events enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
...
Events *event = [NSEntityDescription
    insertNewObjectForEntityForName:@"Events" inManagedObjectContext:context];
event.title = [obj objectForKey:@"title"];
NSSet *categories = [[[NSSet alloc] init] setByAddingObjectsFromArray:[obj objectForKey:@"categories"]];
NSLog(@"CATS %@", categories);
[event addCategories:categories];

最终让核心数据找到相关类别(已经添加到数据库中)并将其附加到事件？

此刻我得到

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFDictionary entity]: unrecognized selector sent to instance 0x893a8c0'

非常感谢任何帮助，谢谢!

Answer 1

categories 是 NSDictionaries 的 NSSet，但是

- (void)addCategories:(NSSet *)values;

需要 NSManagedObject 的 的 NSSet。因此，您必须从每个描述类别的字典中创建一个 NSManagedObject，将它们添加到一个新的 NSSet(或 NSMutableSet)，然后才可以使用新集合调用 addCategories:。