Android Room with RxJava Single<List<T>> compilation error

Question

i’m getting a compilation error “error: Not sure how to convert a Cursor to this method’s return type” when trying to query

Single<List<T>> getList()

but when i change Single to Flowable everything is Ok.

What could be the reason for that error?

Answer 1

Yes, it provides an error, because you are observing for database changes.

Single emits and requires only 1 result. Since it's a wrapper for LiveData which notify as soon as data has been changed, it requires to use Flowable. This allows to get the data in a Stream even if there are currently no data available.

Also take care, that you should not use generics in classes which are generated. this may lead to unwanted behaviour.

If you really want to wrap the data into a Single you may use in your Dao

@Query("SELECT * FROM ActiveShooter") List<ActiveShooter> getAllActiveShooters(); 

and transform your results into a Single within your repository.

public void Single<List<ActiveShooter>> getActiveShooterInRepo() {
     return Single.fromCallable( () -> yourDao.getAllActiveShooters()); 
}

If you do that you'll loose the observability of data changes.