Better way than datasnapshot to retrieve specific data from Firebase for each specific post? Location returned is wrong

Question

Need to retrieve Latitude and Longitude for each specific event from Firebase where the user when creating en event also picks event location (Latitude and Longitude) by setting marker at a specific location.

The problem that I am having is that the last event saved overrides all other existing event locations and so when you hit the TextView to take you to GoogleMaps to show you where the event will be taking place only last event's location saved comes up. But obviously each event has its own specific location.

For example, if I create three events and their locations are Rome, Berlin, and Moscow, the only marker that will be created on GoogleMap will be of event in Moscow because that was the last location saved.

I would like for when the second user hits the TextView using each event-specific postid for that event to be found in the database and for its specific coordinates to show up on the map. Can someone please help me to achieve this? I have been trying to achieve this with datasnapshot, but I haven't been able to find other event locations. I always just get the last event's location saved for all posts. Is there a better way to do it than datasnapshot?

Picture below hope helps clear up how my data structure is organized.

Firebase data structure

MapsActivityUser.java

public class MapsActivityUser extends FragmentActivity implements OnMapReadyCallback {

    private GoogleMap map;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_maps_user);

        SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);
    }

    @Override
    public void onMapReady(GoogleMap googleMap) {
        map = googleMap;

        final DatabaseReference reference = FirebaseDatabase.getInstance().getReference("Posts");
        reference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                    Post post = snapshot.getValue(Post.class);
                    if (post != null) {
                        double latitude = post.getLocation().getLatitude();
                        double longitude = post.getLocation().getLongitude();

                        LatLng location = new LatLng(latitude, longitude);
                        map.addMarker(new MarkerOptions().position(location).title("Event location"));
                        map.moveCamera(CameraUpdateFactory.newLatLngZoom(location, 10));
                    } else {
                        Toast.makeText(MapsActivityUser.this, "Event doesn't have location on Map", Toast.LENGTH_SHORT).show();
                    }
                }
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {

            }
        });
    }
}

Answer 1

The problem in your code is the use of the following line of code:

map.moveCamera(CameraUpdateFactory.newLatLngZoom(location, 10));

Inside the for loop, which basically means that your camera will be moved to the last location that is iterated in the loop. However, if you increase the zoom, you'll be able to see all locations on the map. According to your last comment:

How can I make it so just the marker for the location of that specific event comes up and the others don't?

In this case, you should use a Query. Basically you'll tell Firebase to return only a single location that matches your query. This should look like this:

Query query = reference.orderByChild("locationName").equalTo("locationName");

Now, simply attach a listener on this query and add the marker on the map. In this case is recommended to move the camera to the location, since you get only a single location. But be aware that this query will work if you have unique location names. If you are also storing the id of a location, then you can use only a DatabaseReference that looks like this:

DatabaseReference locationRef = reference.child(locationId);

Attach a listener and add the marker on the map.

Edit:

To get the latitude and longitude, please use the following lines of code:

Query query = reference.orderByChild("postid").equalTo("-LzNDAXtnT6NXYK2XYPK");
ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            double latitude = ds.child("location").child("latitude").getValue(Double.class);
            double longitude = ds.child("location").child("longitude").getValue(Double.class);
            Log.d(TAG, latitude + ", " + longitude);
        }
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        Log.d(TAG, databaseError.getMessage()); //Don't ignore errors!
    }
};
query.addListenerForSingleValueEvent(valueEventListener);

Answer 2

Listen for collection callback (Query Snapshot), inside callback run forloop, there you will get documentchanges class where you will get added, removed, modified indicator this indicates when data added, remove and modified, accordingly perform your logic. to get document use getId where it will return all document id present in collections. I'm not in front of pc, just check on Google.

i'll edit solution soon.