Firebase FirebaseRecyclerAdapter密钥问题

Question

我在项目中使用FirebaseRecyclerAdapter，并且可以通过以下键从firebase中获取数据：

private String title;
private String desc;
private String image;
private String url;
private int id;

但是如果使用此键，我不会从Firebase获取数据

private String classname;
private id classno;

FirebaseRecyclerAdapter代码；

DatabaseReference personsRef = FirebaseDatabase.getInstance().getReference().child("users");
Query personsQuery = personsRef.orderByKey();

mPeopleRV.hasFixedSize();
int numberOfColumns = 1;
RecyclerView.LayoutManager mLayoutManager = new GridLayoutManager(getApplicationContext(), numberOfColumns);
mPeopleRV.setLayoutManager(mLayoutManager);
FirebaseRecyclerOptions personsOptions = new FirebaseRecyclerOptions.Builder<Data>().setQuery(personsQuery, Data.class).build();

mPeopleRVAdapter = new FirebaseRecyclerAdapter<Data, NewsViewHolder>(personsOptions) {
    @Override
    protected void onBindViewHolder(MainActivity.NewsViewHolder holder, final int position, final Data model) {
        holder.setTitle(model.getTitle());
    }

    @Override
    public MainActivity.NewsViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {

        View view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.users_row, parent, false);

        return new MainActivity.NewsViewHolder(view);
    }
};

mPeopleRV.setAdapter(mPeopleRVAdapter);

Data.class

public class Data {

    private String title;
    private String image;
    private int id;

    private String classname;
    private int classno;

    public String getTitle() {
        return title;
    }

    public String getImage() {
        return image;
    }

    public int getId() {
        return id;
    }

    public String getClassname() {
        return classname;
    }

    public int getClassno() {
        return classno;
    }
}

我想使用“ classname”和“ classno”键获取数据。我怎样才能做到这一点？谢谢。