CODEWITHSUNDEEP
javaandroidfirebasefirebase-realtime-database
SAP MCMXCIV
SAP MCMXCIV

Reputation: 11

How to count number of particular child occurrence in firebase for Android in Java

I am making an attendance app and I need to count the particular student attendance from the Firebase. I need to count the number of "prof" occurrence and I am new to this.

enter image description here

 DatabaseReference attendance = FirebaseDatabase.getInstance().getReference("Attendance");
    attendance.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                totaldays++; // total class days
                if(snapshot.child("name").getValue(String.class).equals("prof")){
                    //count no of days present
                }
                Log.e(snapshot.getKey(), snapshot.getChildrenCount() + "");
            }
            Log.e(TAG, totaldays + "");
        }
        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {}
    });

But the result is showing null value.

Upvotes: 1

Views: 1761

Answers (3)

Najaf Ali
Najaf Ali

Reputation: 1473

its very simple to count any field child in the root reference

for example you have a root name attendance then you count to name where type is professor

databaseReference = FirebaseDatabase.getInstance().getReference().child("Attendance").child(istrustnumberavailable);
    databaseReference.limitToFirst(5);

    Query query = databaseReference.orderByChild("name").equalTo("prof");

    ChildEventListener removedListener = query.addChildEventListener(new ChildEventListener() {
        @Override
        public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {

            if (dataSnapshot.exists()){

              long  count=  dataSnapshot.getChildrenCount();


            }


        }

        @Override
        public void onChildChanged(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {

            if (dataSnapshot.exists()){

                long  count=  dataSnapshot.getChildrenCount();


            }


        }

        @Override
        public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) {

            if (dataSnapshot.exists()){

                long  count=  dataSnapshot.getChildrenCount();


            }



        }

        @Override
        public void onChildMoved(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {


        }

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

        }
    });

Upvotes: 0

Alex Mamo
Alex Mamo

Reputation: 138824

In order to solve this, you need to change your database structure. You cannot query your database since your nodes are dynamically generated. As @FrankvanPuffelen mentioned in his comment, the nodes that are causing you troubles are: 04Jul2018 with dcbch... and 05Jul2018 with hello. Because Firebase can only return results that are at a fixed path under each child of the node, to solve this, I recommend you create the date as a property. This is how it can be done and this is how your database structure should look like:

Firebase-root
   |
   --- dcbch..._dkjh...
        |
        --- Prof
             |
             --- email: "[email protected]"
             |
             --- name: "prof"
             |
             --- present: true
             |
             --- date: 1530784439 //Current timestamp

And here is the corresponding query:

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
Query query = rootRef.orderByChild("Prof/name").equalsTo("prof");

Now you can attach a listener and use getChildrenCount() method on the DataSnapshot object to get the number of occurrence.

Upvotes: 1

parag pawar
parag pawar

Reputation: 193

If there is a prof occurrence you can add that child data in a list. In this way you can get the number of childs by using list.size() and also use this list of data in other operations if you have.

Upvotes: 0

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