Table is empty when trying to access the database using RoomDB in Android Studio

Question

getAllLandmarks() returns nothing because table is empty as shown in database inspector. I am trying to set up roomDB in Android Studio and creates googlemap marker by extracting the lang and longitude from the database.

Problem ScreenShot:

What it should look like

MapFragment.java

package com.example.whereswaldo.ui.notifications;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.fragment.app.Fragment;
import androidx.lifecycle.LiveData;

import com.example.whereswaldo.Landmarks;
import com.example.whereswaldo.LandmarksDAO;
import com.example.whereswaldo.R;
import com.example.whereswaldo.database;
import com.example.whereswaldo.databinding.FragmentNotificationsBinding;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.MapsInitializer;
import com.google.android.gms.maps.OnMapReadyCallback;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.CameraPosition;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.Marker;
import com.google.android.gms.maps.model.MarkerOptions;
import com.google.android.material.bottomsheet.BottomSheetDialog;

import java.util.List;

public class MapFragment extends Fragment {

    private FragmentNotificationsBinding binding;

    GoogleMap mGoogleMap;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        View view=  inflater.inflate(R.layout.fragment_notifications, container, false);
        SupportMapFragment supportMapFragment=(SupportMapFragment) getChildFragmentManager().findFragmentById(R.id.google_map);

        // Retrieve landmarks data from the database
        LandmarksDAO landmarksDAO = database.getDatabase(getContext()).landmarksDAO();
        LiveData<List<Landmarks>> landmarksLiveData = landmarksDAO.getAllLandmarks();

        supportMapFragment.getMapAsync(new OnMapReadyCallback() {
            @Override
            public void onMapReady(GoogleMap googleMap) {
                MapsInitializer.initialize(getContext());
                mGoogleMap = googleMap;
                googleMap.setMapType(GoogleMap.MAP_TYPE_NORMAL);

                landmarksLiveData.observe(getViewLifecycleOwner(), landmarks -> {
                    // Loop through the landmarks and create markers
                    for (Landmarks landmark : landmarks) {
                        LatLng position = new LatLng(landmark.getLatitude(), landmark.getLongitude());
                        String title = landmark.getName();

                        googleMap.addMarker(new MarkerOptions().position(position).title(title));

                        CameraPosition cameraPosition = CameraPosition.builder()
                                .target(position)
                                .zoom(16)
                                .bearing(0)
                                .tilt(45)
                                .build();
                        googleMap.moveCamera(CameraUpdateFactory.newCameraPosition(cameraPosition));
                    }
                });
            }
        });

        return view;
    }

    @Override
    public void onDestroyView() {
        super.onDestroyView();
        binding = null;
    }
}

database.java

package com.example.whereswaldo;

import android.content.Context;

import androidx.room.Database;
import androidx.room.Room;
import androidx.room.RoomDatabase;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

@Database(entities = {Landmarks.class}, version = 1, exportSchema = false)
public abstract class database extends RoomDatabase {

    public abstract LandmarksDAO landmarksDAO();

    private static volatile database INSTANCE;
    private static final int NUMBER_OF_THREADS = 4;
    public static final ExecutorService databaseWriteExecutor = Executors.newFixedThreadPool(NUMBER_OF_THREADS);

    public static database getDatabase(final Context context) {
        if (INSTANCE == null) {
            synchronized (database.class) {
                if (INSTANCE == null) {
                    INSTANCE = Room.databaseBuilder(context.getApplicationContext(), database.class, "landmarks").createFromAsset("landmarks.db").build();
                }
            }
        }
        return INSTANCE;
    }
}

LandmarkDAO.java

package com.example.whereswaldo;

import androidx.lifecycle.LiveData;
import androidx.room.Dao;
import androidx.room.Insert;
import androidx.room.OnConflictStrategy;
import androidx.room.Query;
import androidx.room.Update;

import java.util.List;

@Dao
public interface LandmarksDAO {

    @Insert(onConflict = OnConflictStrategy.ABORT)
    public void insert(Landmarks landmarks);

    @Query("SELECT * FROM landmarks")
    LiveData<List<Landmarks>> getAllLandmarks();

    @Query("SELECT * FROM landmarks WHERE Name = :Name")
    LiveData<Landmarks> findLandmark(String Name);
}

I have tried putting Log comments to see where is the problem. It seems i am able to get into the landmarksLiveData.observe(getViewLifecycleOwner(), landmarks -> { but not the for loops afterwards.

I also tried adding this in the getDatabase() from database.java SupportSQLiteDatabase sdb = INSTANCE.getOpenHelper().getWritableDatabase();

Hence, the getAllLandmarks() returns nothing.

I would like to know where is the problem lying? Thank you!

Answer 1

Your getAllLandmarks() function is returning nothing because there is nothing in the database and to add it you must create objects of all the landmarks

Landmarks landmark1 = new Landmarks(Sydney Opera House,Jorn Utzon, Peter Hall,Bennelong Point,Sydney NSW 200......);

Landmarks landmark2 = new Landmarks();

Landmarks landmark3 = new Landmarks(......);

ArrayList<Landmarks> landmarks = new ArrayList<Landmark>();
landmarks.add(landmark1);
landmarks.add(landmark2);
landmarks.add(landmark3);

for(Landmarks landmark : landmarks){
   landmarksDAO.insert(landmark)
}

Add this code before

   supportMapFragment.getMapAsync(new OnMapReadyCallback() {