Recursive Relationship in Realm Model

Question

If I wish to have a Realm array of the same user model, an exception occurs. RLMException(@"RLMArray properties require a protocol defining the contained type - example: RLMArray<Person>."); So is there a workaround? How can a recursive relationship be implemented in Realm as below?

#import <Realm/Realm.h>
@interface User : RLMObject
@property NSInteger userId;
@property NSString *displayName;
@property RLMArray<User> *friends;
- (instancetype)initWithDictionary:(NSDictionary *)data;
@end  
RLM_ARRAY_TYPE (User)

Answer 1

As the exception says, you need to declare a protocol to define the contained type of the RLMArray. This is what the RLM_ARRAY_TYPE macro does. The special thing here is that you need to put this declaration before your interface declaration, which can be done by pre-declaring the User type with @class. You can do it like this :

#import <Realm/Realm.h>

@class User;
RLM_ARRAY_TYPE (User)

@interface User : RLMObject
@property NSInteger userId;
@property NSString *displayName;
@property RLMArray<User> *friends;
- (instancetype)initWithDictionary:(NSDictionary *)data;
@end