Realm realtionships and duplicate data

[Faisal Abid]

Running into some weird issues with duplicate data.

I have 3 tables

Movies

Users

and WatchedByUser

Both movies and users are independent of each other, but when a user does watch a movie. I make a query for the movie object and a query for the user object and add it to a WatchedByUser object.

realm.beginTransaction();

user = realm.where

movie = realm.where

WatchedByUser wbu = new WatchedByUser();

wbu.setUser(user);

wbu.setMovie(movie);

realm.copyToRealm(wbu);

realm.commitTransaction();

All works great. but now in my movie table and user table, there are two copies of the User and Movie.

How do i prevent that from happening? I just want to link the objects, not create copies of it.

[Emanuele Zattin]

Hello Faisal,

that's an interesting use-case!

A couple of notes:

1) In Realm you don't need an extra model class to keep track of many-to-many relationship, as you do in a relational database. All you need is something like this:

Movie:
* title
* RealmList<User> watchers; // you only need this field if you need queries going in the other direction as well

User:
* name
* RealmList<Movie> moviesWatched.

2) The duplication or objects happens because you are using standalone objects to insert the data. SInce primary-keys are not available yet (soon!) there's no way for Realm to know if it's actually the same user and movie you are inserting, so it adds a new one.
Also bear in mind that using standalone objects is a waste of memory.
One way to do it, given for the sake of the argument you want to keep the WatchedByUser class, is something like:

User user = realm.where(User.class)....
Movie movie = realm.where(Movie.class)....

realm.beginTransaction();
WatchedByUser wbu = realm.createObject(WatchedByUser.class);
wbu.setUser(user);
wbu.setMovie(movie);
realm.commitTransaction();

Does this help you?

--
Emanuele Zattin

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[Faisal Abid]

Ah interesting, these are good pointers. I think this helps me out a lot. I'll give it a spin!