Realm, network operations, subscribing and observing on different threads with RxJava

Question

I need to :

• Fetch some data from an API on a background thread
• Display the data on the UI

• Save to Realm.

  fetchItemsFromServer().subscribeOn(Schedulers.io())
          .observeOn(AndroidSchedulers.mainThread()).subscribe(new Action1<ItemList>() {
      @Override
      public void call(ItemList items) {
  
          displayItems(items);
  
          try {
              realm.beginTransaction();
              realm.copyToRealmOrUpdate(itemList);
              realm.commitTransaction();
              Logger.v("Realm ", "Copied list object to realm");
          } catch (Exception e) {
              Logger.e("Realm Something went wrong ", e);
              realm.cancelTransaction();
          }
  
      }
  }
  

This throws an error : realm accessed from incorrect thread

I have 4 tabs fetching different messages at the same time.

fetchItemsFromServer() is an intensive call and confining this call to one thread is not good. I need this flexibility.

Has anyone found any workarounds using realm this way?

Most examples e.g tend to be focused on fetching from Realm vs working with network operations:

Example below:

Rxjava - https://realm.io/news/realm-java-0.87.0/

Using realm with RxJava - https://realm.io/news/using-realm-with-rxjava/ (previous solution but performance drawbacks)

My Realm is provided by a database module through dependency injection (Dagger 2)

@Module
public class DatabaseModule {

    public static final String REALM_FILE_NAME = "Realm name";

    @Provides
    Realm providesRealmInstance(Context context) {
    return Realm.getInstance(
            new RealmConfiguration.Builder(context)
                    .name(REALM_FILE_NAME)
                    .build());
    }
}

Answer 1

Instead of saving data on the UI thread I would do it on the background instead using the following pattern:

fetchItemsFromServer()
    .doOnNext(new Action1<ItemList>() {
        @Override
        public ItemList call(ItemList list) {
            // Save data on the background thread
            Realm realm = Realm.getDefaultInstance();
            realm.beginTransaction();
            realm.copyToRealmOrUpdate(list);
            realm.commitTransaction();
            realm.close();
        }
    })
  .subscribeOn(Schedulers.io())
  .observeOn(AndroidSchedulers.mainThread())
  .subscribe(new Action1<ItemList>() {
    @Override
    public void call(ItemList items) {
        displayItems(items);
    }
}