Retrieve data from several Firebase database reference at the same time in Android

Question

I have several database references. From those, I'm fetching data & then keeping them in a list, example : List<Model>. I am using addValueEventListener() to retrieve data. Can I fetch all the data concurrently or I have to wait until completion of a single reference? What is the perfect way to do this?

It's simple. A root reference having multiple nodes. All the nodes have similar type data (model) , but on different topics. That's why I'm maintaining separate nodes. — Newaj, Nov 04 '18 at 16:36

score 1 · Answer 1 · answered Nov 04 '18 at 16:44

1

You can try something like this.

DatabaseReference ref = FirebaseDatabase.getInstance().getReference();
    ref.addValueEventListener(new ValueEventListener()
    {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot)
        {
            //Node 1: This let's you get data from the first node
            dataSnapshot.child("node1").getValue();

            //Node 2: This let's you get data from the second node
            dataSnapshot.child("node2").getValue();
        }

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

        }
    });

This way you use only 1 reference

answered Nov 04 '18 at 16:44

Janwilx72

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Then addValueEventListener() on every child nodes inside onDataChange()? – Newaj Nov 04 '18 at 16:48
You call ref once. Then in the onDataChange you can use the dataSnapshot to fetch data where you need. You can navigate to the Nodes you want by using the .child() after dataSnapshot. Then use the .getValue() to fetch the data. You don't need to add any more valueEventListeners. You can fetch all the data in 1 – Janwilx72 Nov 04 '18 at 17:41

score 1 · Accepted Answer · answered Nov 05 '18 at 08:24

1

Adding a listener on the root reference, is a very bad idea because everytime something changes in your database, you'll need to download the entire JSON tree and this a waste of bandwidth and resources. To solve this, you can wait for the data that is coming from the database in order to create another query or you can use nested listeners. The nested listeners are a bit convoluted, but the flow itself should be pretty easy to follow. So in case of Firebase, there is nothing wrong about nested listeners.

What is the perfect way to do this?

The "perfect way" in this case, is the case that you are comfortable with.

answered Nov 05 '18 at 08:24

Alex Mamo

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Hi N.K.T! Have you tried my solutions above, does it work? – Alex Mamo Nov 06 '18 at 07:47
Sorry for late response. Thanks for your explanation. – Newaj Nov 06 '18 at 10:01
1

I used a foreach loop for the nodes, there every node has several child nodes. There I populated the list again & again with data from every individual child nodes. – Newaj Nov 06 '18 at 10:10

Retrieve data from several Firebase database reference at the same time in Android

2 Answers2