如何从Firebase中检索包含另一个字符串列表的完整对象列表？

Question

I have stored some List of person objects on Firebase .I want to retrieve this full List into newList of person from database.The class perosn contains another List batch My class person look like:

public class person {
public String name,sid;
public HashMap<String,String> batch;
public int cls;
}

The code I have used is:

    FirebaseDatabase database = FirebaseDatabase.getInstance();
    DatabaseReference fDatabaseRoot = database.getReference("studentsList");
    fDatabaseRoot.orderByChild("name").addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for (DataSnapshot areaSnapshot : dataSnapshot.getChildren()) {
                Map<String,person> td = 
                        (HashMap<String,person>)areaSnapshot.getValue();


               // arrayListStudent= (List<person>) td.values();
                 // Log.d("aaa1",arrayListStudent.toString());
            }
            //Log.d("aaa",arrayListStudent.toString());
        }
        @Override
        public void onCancelled(DatabaseError databaseError) {
        }
    });

Where am i getting wrong.Please give some hint and suggestions.... Here is the screenshot of my database structure:

Answer 1

Please use this code:

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference studentsListRef = rootRef.child("studentsList");
Query query = studentsListRef.orderByChild("name");
ValueEventListener eventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            String name = ds.child("name").getValue(String.class);
            String key1 = ds.child("batch").child("0").getValue(String.class);
            String key2 = ds.child("batch").child("1").getValue(String.class);
            Log.d("TAG", name + " / " + key1 + " / " + key2);
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {}
};
query.addListenerForSingleValueEvent(eventListener);

In this way, you'll get the value of name and of both fields under batch .