Room persistance library. Delete all

Question

You can create a DAO method to do this.

@Dao 
interface MyDao {
    @Query("DELETE FROM myTableName")
    public void nukeTable();
}

As of Room 1.1.0 you can use clearAllTables() which:

Deletes all rows from all the tables that are registered to this database as entities().

If want to delete an entry from the the table in Room simply call this function,

@Dao
public interface myDao{
    @Delete
    void delete(MyModel model);
}

Update: And if you want to delete complete table, call below function,

  @Query("DELETE FROM MyModel")
  void delete();

Note: Here MyModel is a Table Name.

Use clearAllTables() with RXJava like below inorder to avoid java.lang.IllegalStateException: Cannot access database on the main thread since it may potentially lock the UI for a long period of time.

Completable.fromAction(new Action() {
        @Override
        public void run() throws Exception {
            getRoomDatabase().clearAllTables();
        }
    }).subscribeOn(getSchedulerProvider().io())
            .observeOn(getSchedulerProvider().ui())
            .subscribe(new Action() {
                @Override
                public void run() throws Exception {
                    Log.d(TAG, "--- clearAllTables(): run() ---");
                    getInteractor().setUserAsLoggedOut();
                    getMvpView().openLoginActivity();
                }
            }, new Consumer<Throwable>() {
                @Override
                public void accept(Throwable throwable) throws Exception {
                    Log.d(TAG, "--- clearAllTables(): accept(Throwable throwable) ----");
                    Log.d(TAG, "throwable.getMessage(): "+throwable.getMessage());


                }
            });

I had issues with delete all method when using RxJava to execute this task on background. This is how I finally solved it:

@Dao
interface UserDao {
    @Query("DELETE FROM User")
    fun deleteAll()
}

and

fun deleteAllUsers() {
    return Maybe.fromAction(userDao::deleteAll)
        .subscribeOn(Schedulers.io())
        .observeOn(AndroidSchedulers.mainThread())
        .subscribe ({
            d("database rows cleared: $it")
        }, {
            e(it)
        }).addTo(compositeDisposable)
}

This is how we do it from a Fragment.

fun Fragment.emptyDatabase() {
    viewLifecycleOwner.lifecycleScope.launchWhenCreated {
        withContext(Dispatchers.IO) {
            Database.getInstance(requireActivity()).clearAllTables()
        }
    }
}

If you are emptying the database from an activity use this:

fun Activity.emptyDatabase() {
    // create a scope to access the database from a thread other than the main thread
    val scope = CoroutineScope(Dispatchers.Default)
    scope.launch {
        SitukaDatabase.getInstance(this@emptyDatabase).clearAllTables()
    }
}

It could also be possible to call the clearAllTables method from the main thread. I haven't tried it out but I noticed that Android Studio does not recognize the call as a suspend function.