How to send multiple queries to firebase database at once in android without putting in a loop

Question

I am trying to query the database to check through multiple unrelated keys to check a parameter and compile a list that fits my conditions.

I already have a list which was created with a previous query to another node of the database. Which returned a list of keys which i want to check.

Now i want to iterated through this list and query them to see if they fit my conditions.

I have tried downloading whole node and checking client side but this would become very slow if the node grows and download a lot of unnecessary data.

I have tried putting a loop around my query and sending multiple queries within, on the keys in my list. This worked but becomes increasingly complicated as i try to go back to the beginning with different conditions if my original conditions were not met.

for (int i = 0; i < nextUp.size(); i++) {
    Query query = myRef.child(nextUp.get(i).toString());
    query.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            boolean v = false;

            for (DataSnapshot likesSnapshot : dataSnapshot.getChildren()) {
                if (uid.equals(likesSnapshot.getKey())) {
                    v = true;
                } else {
                }

                //b if for second pass with different conditions
                if (b) {
                    if (!v) {
                        complieList(dataSnapshot.getKey(), b);
                    }

                    if (!b) {
                        complieList(dataSnapshot.getKey(), b);
                    }
                }

            }

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

                }
            });
}

By the time my code goes back to the beginning all the queries have not yet complete. So i need to wait for all to finish to continue. But as this requires waiting for the results for many queries i cannot simply put it in the onDataChange. I have seen that a JavaScript promise can send multiple queries at once in a pipeline and receive the result for all of them. Is there a way to do this in Java.

Update

Here is a link to what i want to do but it is for javascript Querying By Multiple Keys in Firebase

Answer 1

Did you consider using transaction?

Transaction is used to composite serveral db request and request one time.

It is also used to prevent data change during db request.

https://firebase.google.com/docs/reference/android/com/google/firebase/database/Transaction.Handler?hl=ko

by the way, realtime db doesn’t support complicate query

you can use only orderbychild.. etc

But you can store data separately when data is saved.