Get values from Firebase Database on basis of two key values

Question

I'm developing an android application using JAVA and FIREBASE. I've stored user details in Firebase Realtime Database.

My problem is first I want to access all the students based on their course and year. For example I want to retrieve students who opted course BCA and are in year 1st. I don't know how to achieve this.

here is my code.

Main Activity

public class MainActivityStudentList extends AppCompatActivity {

    private Button year1,year2,year3;
    private RecyclerView studentRecyclerView;
    private String branch,year = "1";

    private DatabaseReference databaseReference;
    private Query query;

    private ShowStudentsAdapter showStudentsAdapter;
    private List<AddStudents> addStudents;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_show_list);

        assert getSupportActionBar() != null;
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);

        branch = getIntent().getStringExtra("branch");

        year1 = findViewById(R.id.button1);
        year2 = findViewById(R.id.button2);
        year3 = findViewById(R.id.button3);

        year1.setText("YEAR 1");
        year2.setText("YEAR 2");
        year3.setText("YEAR 3");

        studentRecyclerView = findViewById(R.id.showRecyclerView);

        studentRecyclerView.setHasFixedSize(true);
        studentRecyclerView.setLayoutManager(new LinearLayoutManager(this));
        addStudents = new ArrayList<>();

        databaseReference = FirebaseDatabase.getInstance().getReference("STUDENTS");

        getData();

        year1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                year1.setBackgroundColor(getResources().getColor(R.color.white));
                year2.setBackgroundColor(getResources().getColor(R.color.lightBlue));
                year3.setBackgroundColor(getResources().getColor(R.color.lightBlue));
                addStudents.clear();
                year = "1";
                getData();
            }
        });

        year2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                year1.setBackgroundColor(getResources().getColor(R.color.lightBlue));
                year2.setBackgroundColor(getResources().getColor(R.color.white));
                year3.setBackgroundColor(getResources().getColor(R.color.lightBlue));
                addStudents.clear();
                year = "2";
                getData();
            }
        });

        year2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                year1.setBackgroundColor(getResources().getColor(R.color.lightBlue));
                year2.setBackgroundColor(getResources().getColor(R.color.lightBlue));
                year3.setBackgroundColor(getResources().getColor(R.color.lightBlue));
                addStudents.clear();
                year = "3";
                getData();
            }
        });
    }

    @Override
    public void onBackPressed() {
        super.onBackPressed();
        addStudents.clear();
    }

    private void getData(){
        query = databaseReference.orderByChild("course").equalTo(branch);
        query.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                for (DataSnapshot dataSnapshot1 : dataSnapshot.getChildren()) {
                        AddStudents addStudent = dataSnapshot1.getValue(AddStudents.class);
                        addStudents.add(addStudent);
                }
                LinearLayoutManager linearLayoutManager = new LinearLayoutManager(MainActivityStudentList.this);
                linearLayoutManager.setReverseLayout(true);
                linearLayoutManager.setStackFromEnd(true);
                studentRecyclerView.setLayoutManager(linearLayoutManager);
                showStudentsAdapter = new ShowStudentsAdapter(MainActivityStudentList.this, addStudents);
                studentRecyclerView.setAdapter(showStudentsAdapter);
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
                Toast.makeText(MainActivityStudentList.this, databaseError.getMessage(), Toast.LENGTH_SHORT).show();
            }
        });
    }
}

Adapter class

public class ShowStudentsAdapter extends RecyclerView.Adapter<ShowStudentsAdapter.showStudentViewHolder> {

    private Context dContext;
    private List<AddStudents> addStudents;

    public ShowStudentsAdapter(Context context,List<AddStudents> addStudent){
        dContext = context;
        addStudents = addStudent;
    }

    @NonNull
    @Override
    public showStudentViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View v = LayoutInflater.from(dContext).inflate(R.layout.show_faculty_cardview,parent,false);
        return new showStudentViewHolder(v);
    }

    @Override
    public void onBindViewHolder(@NonNull showStudentViewHolder holder, int position) {
        AddStudents dAddStudent = addStudents.get(position);
        holder.name.setText(dAddStudent.getName());
        holder.course.setText(dAddStudent.getCourse());
        holder.year.setText(dAddStudent.getYear());
    }

    @Override
    public int getItemCount() {
        return addStudents.size();
    }

    public class showStudentViewHolder extends RecyclerView.ViewHolder{
        TextView name,course,year;
        ImageView delete;

        public showStudentViewHolder(@NonNull View itemView) {
            super(itemView);
            name = itemView.findViewById(R.id.fName);
            course = itemView.findViewById(R.id.fEmail);
            year = itemView.findViewById(R.id.fPosition);
            delete = itemView.findViewById(R.id.fDelete);
        }
    }
}

I have 3 buttons in main activity called year1,year2,year3 when i click on year1 i want to display all BCA students who are in year 1st and same goes to other buttons.

Any help would be great.

Answer 1

you can do it by filtering the list.

List<AddStudents> addStudentFilterd = new ArrayList<AddStudents>();

        for (int i = 0; i < addStudent.size(); i++) {
           if( addStudent.get(i).getCourse.equals("BCA") &&  addStudent.get(i).getYear.equals("1")){
            addStudentFilterd.add(addStudent.get(i));
        }

Pass the filtered list to the adaptor on button click, finally .notifyDataSetChanged(); .