How to use a data from one table as a reference to get another data in another table using Firebase?

Kim E. R Published at Dev

Kim E. R

I just retrieve a list of data from a table named 'appointment'. From this table, I will need to get a data named 'theraid' in order to get the name from another table named 'thera'. I have no idea how to do it in android java. Is there someone can guide me? Thanks in advance.

Here is my table structure in firebase

Here is my code, but it does not work for me. Java class

 databaseReference= FirebaseDatabase.getInstance().getReference().child("appointment");

        databaseReference.orderByChild("userid").equalTo(userid1).addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {


                for(DataSnapshot dataSnapshot1: dataSnapshot.getChildren()) {

                    AppointmentObject thera= dataSnapshot1.getValue(AppointmentObject.class);
                    String tid = dataSnapshot.child("theraid").getValue(String.class);

                    a.add(thera);

                     refThera = FirebaseDatabase.getInstance().getReference("alluser").child("thera");
                    refThera.child(tid).addValueEventListener(new ValueEventListener() {
                        @Override
                        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                            for(DataSnapshot dataSnapshot2: dataSnapshot.getChildren()) {
                                String text = dataSnapshot2.child("name").getValue(String.class);
                                tname.add(text);

                        }}

                        @Override
                        public void onCancelled(@NonNull DatabaseError databaseError) {
                            Toast.makeText(getApplicationContext(), "Oh no!", Toast.LENGTH_SHORT).show();
                            throw databaseError.toException();
                        }
                    });
                }


            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
                Toast.makeText(getApplicationContext(), "Oh no!", Toast.LENGTH_SHORT).show();
            }
        });

        adapter=new MyRecyclerviewPAppointment(MainActivityPAppointment.this, a,tname);
        rv.setAdapter(adapter);

RecyclerView class


    @Override
    public void onBindViewHolder(@NonNull final MyRecyclerviewPAppointment.MyViewHolder holder, int position) {
        holder.tname.setText(name.get(position).charAt(position));
        holder.tdate.setText(alist.get(position).getDate());
        holder.ttime.setText(alist.get(position).getTiming());

    }

Peter Haddad

Try the following:

 databaseReference = FirebaseDatabase.getInstance().getReference().child("appointment");

        databaseReference.orderByChild("userid").equalTo(userid1).addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                for(DataSnapshot dataSnapshot1: dataSnapshot.getChildren()) {
                    String theraid = dataSnapshot1.child("theraid").getValue(String.class);

                    DatabaseReference refThera = FirebaseDatabase.getInstance().getReference().child("alluser").child("thera");
                    refThera.child(theraid).addValueEventListener(new ValueEventListener() {
                    @Override
                   public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                       String name = dataSnapshot.child("name").getValue(String.class);
                       }

                    @Override
                 public void onCancelled(@NonNull DatabaseError databaseError) {
                      Toast.makeText(getApplicationContext(), "Oh no!", Toast.LENGTH_SHORT).show();
                      throw databaseError.toException(); 
                    }
              });


               }
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
                Toast.makeText(getApplicationContext(), "Oh no!", Toast.LENGTH_SHORT).show();
                throw databaseError.toException();
            }
        });

First retreive the theraid inside the appointment node then add another databaseReference and use the theraid to be able to retrieve the name.

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