Inverse Relationships. about realm-swift HOT 11 CLOSED

Bidirectional relationships must be explicitly linked at this time. Here's an example:

@interface Item : RLMObject
@property Box *box;
@end

RLM_ARRAY_TYPE(Item);

@interface Box : RLMObject
@property RLMArray<Item> *items;
@end

...

Item *item = [[Item alloc] init];
Box *box = [[Box alloc] initWithObject:@[@[item]]];
item.box = box;

We have plans to simplify this pattern in the future.

from realm-swift.

Good to know, and this is the path that I already took. I was also trying to design a way to produce inverse relationship logic by incorporating preprocessor macros that would overload addObject, removeObject methods with the added functionality to set a value for the inverse property.

However the design of RLMArray holding it's own mutation methods makes this hard to do, as I can't add these mutation methods on the class itself.

Is there any design propositions within the realm team on how this will be simplified?

from realm-swift.

We are still at the early stages of discussion. The good news is that the functionality needed to support multi-directional relationships are already in the code base. It seems likely at this point that we will add a method to expose/fetch inverse relationship values without having to add an explicit property. This may put some limitations on what you can do (such as keypath queries on inverse relationships) but greatly simplifies the task of specifying multi-direction relationships on your models.

from realm-swift.

If I create a bidirectional relationship explicitly linked, as @jpsim mentions with the same example I get an error "Unknown type name 'Box'". Am I missing something? Thanks

from realm-swift.

You have to forward-declare the Box type with @class Box;

from realm-swift.

What should I do when I have 3 objects related like this:

@interface Comment : RLMObject
@property NSNumber *createdTime;
@property NSString *text;
@property User *fromUser;
@property Media *fromMedia;
@end

RLM_ARRAY_TYPE(Comment)

@interface Media : RLMObject
@property NSNumber *created_time;
@property NSString *standard_relutionURL;
@property RLMArray<Comment> *comments;
@property Comment *caption;
@property User *fromUser;
@end

RLM_ARRAY_TYPE(Media)

@interface User : RLMObject
@property NSString *full_name;
@property NSString *profile_pictureURL;
@property NSString *username;
@property RLMArray<Media> *medias;
@property RLMArray<Comment> *comments;
@end

RLM_ARRAY_TYPE(User)

If I forward-declare User type with @class User; I still get Unknown type for Media in the interface of Comment.

from realm-swift.

Forward declare Media as well.

from realm-swift.

Has there been any progress on this? Doing this with remote JSON data is very tedious

from realm-swift.

+1

from realm-swift.

We have had a few discussions on the design for this. Ideally we would like to provide the ability to declare a property as an the inverse of a property on another model. Unfortunately this would imply full query support which is a fairly large task and will take a long time to make work properly.

In the shorter term it would be possible to at least expose object and array property backlink information which is already stored internally in Realm. If we exposed this it would most likely be a method on RLMObject which returns all other objects which link to it (either using an RLMObject or RLMArray property). This is probably something that we could make work pretty quickly if it would be useful.

from realm-swift.

This would be very handy. It would be absolutely sufficient for all my current needs.

from realm-swift.