Realm-cocoa: Many to Many realtions problem

[ggirotto]

Im trying to create two Realm Objects: UserObject and GroupObject. The problem is that i have a many to many realtionship between them, where the user has n groups and each group has n users. First I got stuck into the interdependency problem, which one has the answer here First Answer and here Second Answer.

I followed the instructions and stored all interfaces and implementations inside the same file, but now I'm having the following error:

'RLMException', reason: 'Property 'groups' requires a protocol defining the contained type - example: RLMArray.'

Some of my Realm Objects code:

#import <Realm/Realm.h>
@class HSGroup;
@class HSUser;

RLM_ARRAY_TYPE(GroupObject);
RLM_ARRAY_TYPE(UserObject);

@interface GroupObject : RLMObject
@end

@interface UserObject : RLMObject
@end

@interface GroupObject ()

@property NSString *groupId;
@property NSNumber<RLMDouble> *latitude;
@property NSNumber<RLMDouble> *longitute;
@property RLMArray<UserObject *> *members;
@property NSString *groupName;
@property NSString *imageURL;
@property NSDate *modifiedAt;

-(instancetype)initWithGroup:(HSGroup *)group;

@end

@interface UserObject ()

@property NSString *userIdentifier;
@property NSString *name;
@property NSNumber<RLMDouble> *actualLatitude;
@property NSNumber<RLMDouble> *actualLongitute;
@property RLMArray<GroupObject *> *groups;
@property NSString *imageURL;
@property NSDate *modifiedAt;

-(instancetype)initWithUser:(HSUser *)user;

@end

Realm framework version: latest

Xcode version: 8.3.3

iOS/OSX version: 10.12.6

[bdash]

@property RLMArray<UserObject *> *members;

should be

@property RLMArray<UserObject><UserObject *> *members;

And similarly for your other RLMArray properties.

The former declares an RLMArray that is constrained via Objective-C lightweight generics to contain only UserObjects. Objective-C generics are type-erased, meaning that information about their types is not available at runtime. The latter declares an RLMArray that both uses Objective-C generics and conforms to a UserObject protocol (the protocol is created by the RLM_ARRAY_TYPE macro). Information about protocol conformance _is_ available at runtime, and is what Realm Objective-C looks at to determine what object type your array property contains.

[ggirotto]

Nice explanation. But what about Protocol qualifiers must precede type arguments error? Do you know how to solve it?

[bdash]

Sorry, I typed that on my phone and neglected to double-check the order of the protocol vs generic constraint. It should be reversed from what I said:

@property RLMArray<UserObject *><UserObject> *members;

[ggirotto]

That worked perfectly. Thank you 😄

[bdash]

Glad to hear it!