Flowable from Room database

Hi! Today I’ll tell you how to get data from Room database in reactive way.

Before starting make sure you have following in your build.gradel:

// Room components
implementation "android.arch.persistence.room:runtime:$rootProject.roomVersion"
implementation "android.arch.persistence.room:rxjava2:$rootProject.roomVersion"
annotationProcessor "android.arch.persistence.room:compiler:$rootProject.roomVersion"
androidTestImplementation "android.arch.persistence.room:testing:$rootProject.roomVersion"

// Lifecycle components
implementation "android.arch.lifecycle:extensions:$rootProject.archLifecycleVersion"
implementation "android.arch.lifecycle:reactivestreams:$rootProject.archLifecycleVersion"
annotationProcessor "android.arch.lifecycle:compiler:$rootProject.archLifecycleVersion"

// Rx
implementation 'io.reactivex.rxjava2:rxandroid:2.1.0'
implementation 'io.reactivex.rxjava2:rxjava:2.2.1'

First we need to get database from assets and define Dao class for data.

@Database(entities = {Verse.class}, version = 1, exportSchema = false)
public abstract class MyRoomDatabase extends RoomDatabase {
    public abstract MyDataDao myDataDao();

    private static MyRoomDatabase INSTANCE;

    static MyRoomDatabase getDatabase(final Context context) {
        if (INSTANCE == null) {
            synchronized (MyRoomDatabase.class) {
                if (INSTANCE == null) {
                    INSTANCE = Room.databaseBuilder(context.getApplicationContext(),
                            MyRoomDatabase.class, "data.sqlite3") // get db from assets
                            .openHelperFactory(new AssetSQLiteOpenHelperFactory())

        return INSTANCE;

    public void destroyInstance() {
        synchronized (MyRoomDatabase.class) {
            INSTANCE = null;

public interface MyDataDao {

    @Query("SELECT * from verses ORDER BY RANDOM() LIMIT 1")
    LiveData<Verse> getRandomVerse();

    @Query("SELECT * from verses ORDER BY RANDOM() LIMIT 1")
        // same request
    Flowable<Verse> getRxRandomVerse();

Above code represents raw request for random Verse objects from database table verses
What I like about Room is it allows us to get Rx Flowable as well as LiveData objects out of the box!
In our case we will use Flowable.
Next, define a repository class:

class MyRepository(context: Context?) {

    private val mDataDao: MyDataDao
    private val db: MyRoomDatabase? = MyRoomDatabase.getDatabase(context)

    init {
        mDataDao = db!!.myDataDao()

    fun getRxRandomVerse(): Flowable<Verse> {
        return mDataDao.getRxRandomVerse

    fun getDb(context: Context?): MyRoomDatabase? {
        return db ?: MyRoomDatabase.getDatabase(context)

    fun closeDb() {

Finally, let’s extract data onto presentation layer:

class MainActivityPresenter {

    private var mRepository: MyRepository? = null

    fun attach(mainActivityView: MainActivityView, context: Context) {
        this.mainActivityView = mainActivityView
        this.mRepository = MyRepository(context)

    fun getRandomVerse() {
                .subscribe({ verse ->
                }, { error ->

class MainActivity : MainActivityPresenter.MainActivityView {


    override fun updateUI(verse: String) {
        textViewVerse.text = verse


That’s all in general. Pretty simple and handy. I’ve successfully implemented this code in a new random quote app

If you have any questions, leave in comments below.

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