How to combine Retrofit 2 with Realm and RxJava - multithreading

Question

I want to save retrofit responses to realm on the background thread then pass it to the UI Thread, but its a bit tricky since Realm is very touchy with threads. so the code would look like something like this, please submit your edits to all better solutions :)
restApi.userRealmList()
.doOnNext(userRealmModels -> {
if (userRealmModels != null){
mRealm = Realm.getInstance(mContext);
mRealm.asObservable()
.map(realm -> mRealm.copyToRealmOrUpdate(userEntity))
.subscribe(new Subscriber<Object>() {
#Override
public void onCompleted() {
}
#Override
public void onError(Throwable e) {
e.printStackTrace();
}
#Override
public void onNext(Object o) {
Log.d("RealmManager", "user added!");
}
});
}})
.map(userEntityDataMapper::transformAll)
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(new Subscriber<List<User>>() {
#Override
public void onCompleted() {
hideViewLoading();
}
#Override
public void onError(Throwable e) {
hideViewLoading();
showErrorMessage(new DefaultErrorBundle((Exception) e));
showViewRetry();
}
#Override
public void onNext(List<User> users) {
showUsersCollectionInView(users);
}
});

Answer 1

You code doesn't look like it can compile? E.g. what is userEntity. Also your copyToRealmOrUpdate isn't inside an transaction, so that will also crash, but it has nothing to do with threads.
If you want to save some data as a side-effect before sending it to the UI, you should be able to do the following:
restApi.userRealmList()
.doOnNext(userRealmModels -> {
if (userRealmModels != null) {
Realm realm = Realm.getInstance(mContext);
realm.beginTransaction();
realm.copyToRealmOrUpdate(userRealmModels);
realm.commitTransaction();
realm.close();
}})
.map(userEntityDataMapper::transformAll)
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(new Subscriber<List<User>>() {
#Override
public void onCompleted() {
hideViewLoading();
}
#Override
public void onError(Throwable e) {
hideViewLoading();
showErrorMessage(new DefaultErrorBundle((Exception) e));
showViewRetry();
}
#Override
public void onNext(List<User> users) {
showUsersCollectionInView(users);
}
});