如何从具有多个节点的 firebase 中检索数据？

Question

I can't resolve this problem: When i try to retrieve data from firebase, it says that there are not setter/field for [Node name] on class [Class name].

My class is "Ricetta" and Every node is named with the name of ricetta.

Ricetta.class

public class Ricetta {

    private String nome;
    private String descrizione;
    private int difficolta;
    private double minuti;
    private String passaggi;
    private String tipologia;
    private String autore;
    private List<Ricetta> ricette;

    public Ricetta(){}

    public List<Ricetta> getRicette() {
        return ricette;
    }

    public void setRicette(List<Ricetta> ricette) {
        this.ricette = ricette;
    }

    public Ricetta(String nome, String descrizione, String tipologia) {
        this.nome = nome;
        this.descrizione = descrizione;
        this.tipologia = tipologia;
    }

    public Ricetta(String nome, String descrizione, String tipologia, String autore, int difficolta, double minuti) {
        this.nome = nome;
        this.descrizione = descrizione;
        this.tipologia = tipologia;
        this.autore = autore;
        this.minuti = minuti;
        this.difficolta = difficolta;
    }


    public String getAutore() {
        return autore;
    }

    public void setAutore(String autore) {
        this.autore = autore;
    }

    public void setDifficolta(int difficolta) {
        this.difficolta = difficolta;
    }

    public void setMinuti(double minuti) {
        this.minuti = minuti;
    }

    public void setTipologia(String passaggi) {
        this.passaggi = passaggi;
    }

    public void setNome(String nome) {
        this.nome = nome;
    }

    public void setDescrizione(String descrizione) {
        this.descrizione = descrizione;
    }

    public void setPassaggi(String passaggi) {
        this.passaggi = passaggi;
    }

    public String getNome() {
        return nome;
    }

    public String getDescrizione() {
        return descrizione;
    }

    public int getDifficolta() {
        return difficolta;
    }

    public double getMinuti() {
        return minuti;
    }

    public String getPassaggi() {
        return passaggi;
    }

    public String getTipologia() {
        return tipologia;
    }

}

OnCreateView method of my HomeFragment.java

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    final FirebaseDatabase database = FirebaseDatabase.getInstance("https://cookbook-e6f41-default-rtdb.europe-west1.firebasedatabase.app/");
    FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
    DatabaseReference ref = database.getReference().child("users");
    ArrayList<Ricetta> ricette = new ArrayList<>();
    ArrayList<User> utenti = new ArrayList<>();
    View v = inflater.inflate(R.layout.fragment_home, container, false);
    LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity());

    ref.addChildEventListener(new ChildEventListener() {
        @Override
        public void onChildAdded(@NonNull DataSnapshot snapshot, @Nullable String previousChildName) {
           Ricetta r = snapshot.child("ricette").getValue(Ricetta.class);
           System.out.println(r.getAutore());
        }

        @Override
        public void onChildChanged(@NonNull DataSnapshot snapshot, @Nullable String previousChildName) {

        }

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

        }

        @Override
        public void onChildMoved(@NonNull DataSnapshot snapshot, @Nullable String previousChildName) {

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            System.out.println("The read failed: " + databaseError.getCode());
        }
    });


    RecyclerView recyclerView = (RecyclerView) v.findViewById(R.id.rv);
    RecyclerViewAdapter adapter = new RecyclerViewAdapter(this.getContext(), ricette);
    recyclerView.setAdapter(adapter);
    recyclerView.setHasFixedSize(true);
    recyclerView.setLayoutManager(layoutManager);
    return v;
}

When i run this is shown:

No setter/field for oooooooooo found on class com.cookbook.Ricetta
No setter/field for qweqw found on class com.cookbook.Ricetta
No setter/field for dfsdfs found on class com.cookbook.Ricetta
No setter/field for 9999 found on class com.cookbook.Ricetta
No setter/field for dfsdfdsf found on class com.cookbook.Ricetta
No setter/field for uuuuuuuuu found on class com.cookbook.Ricetta

Answer 1

You're attaching a ChildEventListener on /users . This means that your onChildAdded is called with the direct child nodes of users, which is m50... in your screenshot. Then you read the value of the ricette child under there, which leads to all the 9999 , dfsdfdf , etc nodes under there.

My guess it that you're trying to read one or all child nodes under ricette , for which you'll need to loop over the child nodes of the snapshot with:

ref.addChildEventListener(new ChildEventListener() {
    @Override
    public void onChildAdded(@NonNull DataSnapshot snapshot, @Nullable String previousChildName) {
       for (DataSnapshot childSnapshot: snapshot.child("ricette").getChildren()) {
           Ricetta r = childSnapshot.getValue(Ricetta.class);
           System.out.println(r.getAutore());
       }
    }

Answer 2

reference.addChildEventListener(new ChildEventListener() {
    @Override
    public void onChildAdded(@NonNull DataSnapshot snapshot, @Nullable String previousChildName) {
       for (DataSnapshot s: snapshot.child("ricette").getChildren()) {
           Ricetta r = s.getValue(Ricetta.class);
Log.d("data",r.getAutore());
        
       }
    }