Can I retrieve two documents from the database in

Question

I'm writing an app in Android Studio. It connects to Firebase Firestore.

The data is structured like this (I've removed the irrelevant bits, for clarity):

Boxes
   - box1
      - grid_id
      - table_id
   -box2
      - grid_id
      - table_id
Grids
    - grid1
    - grid2
Tables
   - table1
   - table2

So, each time I retrieve a box, I also need to retrieve the corresponding Grid and Table.

In my Activity, I have the following:

public class BoxViewActivity {

   String box_id;
   Box box;
   FirebaseFirestore databaseRef;
   BoxFragment boxFragment;
   GridFragment gridFragment;
   TableFragment tableFragment;
   FragmentManager fragmentManager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_edit_box);
        fragmentManager = getSupportFragmentManager();
        boxFragment = fragmentManager.findFragmentById(R.id.fragment_box);

        // Retrieve Box from database and set it up
        Intent intent = getIntent();
        box_id = intent.getStringExtra("BoxId");
        box = new Box();

        databaseRef = FirebaseFirestore.getInstance();

        boxDocRef = databaseRef.collection("boxes").document(box_id);
        boxDocRef.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
            @Override
            public void onComplete(@NonNull Task<DocumentSnapshot> task) {
                if (task.isSuccessful()) {
                    DocumentSnapshot document = task.getResult();
                    if (document.exists()) {
                        // Set up Box
                        box = document.toObject(Box.Class);
                        if (box != null) {
                            // Set up some box views
                        }
                        // Get grid/table key
                        setUpGrid(box.getGridId());
                        setUpTable(box.getTableId());
                    }
                }
            }
        });
    }

    private void setUpGrid(String gridId) {

        DocumentReference gridRef = databaseRef.collection("grids").document(gridId);

        gridRef.addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {

            @Override
            public void onComplete(@NonNull Task<DocumentSnapshot> task) {
                if (task.isSuccessful()) {
                    DocumentSnapshot document = task.getResult();
                    if (document.exists()) {
                        // Retrieve Grid
                        Grid grid= document.toObject(Grid);
                        if (grid != null) {
                            boxFragment.setGrid(grid);
                        }
                    }
                }
            }
        });
    }

    private void setUpTable(String tableId) {
        if(tableId == null) return;

        DocumentReference tableRef = databaseRef.collection("tables").document(tableId);

        tableRef.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {

            @Override
            public void onComplete(@NonNull Task<DocumentSnapshot> task) {
                if (task.isSuccessful()) {
                    DocumentSnapshot document = task.getResult();
                    if (document.exists()) {
                        Table table = document.toObject(Table.Class);
                        if (table != null) {
                            boxFragment.setTable(table);
                        }
                    }
            }
        });
    }

}

The problem I'm having is that the app seems to 'freeze' and then restart when I hit this activity. The screen goes blank and unresponsive, and then the app restarts. Android Studio isn't throwing any errors, and the debug console has nothing. I suspect it's because I'm retrieving the grid and table simultaneously - would that slow it down? If so, what's a better way to do it? Or have I missed something else?

Answer 1

To solve this, I suggest you add a Grid and a Table object within a Box object. In this way you'll be able to a use a single listener instead of three. So your code should look like this:

boxDocRef = databaseRef.collection("boxes").document(box_id);
boxDocRef.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
    @Override
    public void onComplete(@NonNull Task<DocumentSnapshot> task) {
        if (task.isSuccessful()) {
            DocumentSnapshot document = task.getResult();
            FragmentManager fragmentManager = getSupportFragmentManager();
            BoxFragment boxFragment = fragmentManager.findFragmentById(R.id.fragment_box);
            if (document.exists()) {
                // Set up Box
                box = document.toObject(Box.Class);
                if (box != null) {
                    // Set up some box views
                    // Get grid/table key
                    Grid grid = box.getGrid();
                    boxFragment.setGrid(grid);
                    Table table = box.getTable();
                    boxFragment.setTable(table);
                }
            }
        }
    }
});

And remove the declaration of your FragmentManager and BoxFragment. Both should only be present inside the onComplete() method.