How to Efficiently Select Random Products from a Large Firebase Database in Node?

Getting Unique Random Products in Node Firebase

To retrieve a single random product from a node database over 1000 records, consider two approaches: the classic solution and a denormalized approach.

Classic Solution

<br>ListView listView = (ListView) findViewById(R.id.list_view);<br>ArrayAdapter arrayAdapter = new ArrayAdapter<>(context, android.R.layout.simple_list_item_1, randomProductList);<br>listView.setAdapter(arrayAdapter);<br>DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();<br>DatabaseReference productsRef = rootRef.child("products"); //Added call to .child("products")<br>ValueEventListener valueEventListener = new ValueEventListener() {</p>
<pre class="brush:php;toolbar:false">@Override
public void onDataChange(DataSnapshot dataSnapshot) {
    List<String> productList = new ArrayList<>();
    for(DataSnapshot ds : dataSnapshot.getChildren()) {
        String name = ds.child("name").getValue(String.class);
        productList.add(name);
    }

    int productListSize = productList.size();
    List<String> randomProductList = new ArrayList<>();

    randomProductList.add(new Random().nextInt(productListSize)); //Add the random product to list
    arrayAdapter.notifyDatasetChanged();
}

@Override
public void onCancelled(DatabaseError databaseError) {
    Log.d(TAG, "Error: ", task.getException()); //Don't ignore errors!
}

};
productsRef.addListenerForSingleValueEvent(valueEventListener);

This approach loops through all product nodes, adds their names to a list, and randomly selects one.

Denormalized Approach

Create a separate "productIds" node to avoid downloading large amounts of data:

<br>Firebase-root<br>   |<br>   --- products<br>   |     |<br>   |     --- productIdOne<br>   |     |      |<br>   |     |      --- //details<br>   |     |<br>   |     --- productIdTwo<br>   |            |<br>   |            --- //details<br>   |      <br>   --- productIds</p>
<pre class="brush:php;toolbar:false">      |
      --- productIdOne: true
      |
      --- productIdTwo: true
      |
      --- //And so on

<br>DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();<br>DatabaseReference productIdsRef = rootRef.child("productIds");<br>ValueEventListener valueEventListener = new ValueEventListener() {</p>
<pre class="brush:php;toolbar:false">@Override
public void onDataChange(DataSnapshot dataSnapshot) {
    List<String> productIdsList = new ArrayList<>();
    for(DataSnapshot ds : dataSnapshot.getChildren()) {
        String productId = ds.getKey();
        productIdsList.add(productId);
    }

    int productListSize = productList.size();
    List<String> randomProductList = new ArrayList<>();

    DatabaseReference productIdRef = rootRef.child("products").child(productIdsList.get(new Random().nextInt(int productListSize));
    ValueEventListener eventListener = new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            String name = dataSnapshot.child("name").getValue(String.class);
            Log.d("TAG", name);
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            Log.d(TAG, "Error: ", task.getException()); //Don't ignore errors!
        }
    };
    productIdRef.addListenerForSingleValueEvent(eventListener);
}

@Override
public void onCancelled(DatabaseError databaseError) {
    Log.d(TAG, "Error: ", task.getException()); //Don't ignore errors!
}

};
productIdsRef.addListenerForSingleValueEvent(valueEventListener);

This approach queries the "productIds" node to get a random product ID, then queries the "products" node for specific details.

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