ios - iOS核心数据-向实体添加相关数据

iOS初学者在这里。

给定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

与哪个有关

@interface Categories : NSManagedObject

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

@end

并具有一些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];

最终获取核心数据以找到相对类别（已添加到数据库）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'

任何帮助将不胜感激，谢谢！

最佳答案

categories是NSSet的NSDictionaries，但是

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

期望NSSet为NSManagedObject's。因此，您必须从描述类别的每个字典中创建一个NSManagedObject，将它们添加到新的NSSet（或NSMutableSet）中，然后才使用新的集合调用addCategories:。