I cannot enter data and query the database DAO in android studio

Question

Hi i am disperate student and i don't understand why i can't add data and query my the database DAO.

@Entity
public class User {

@ColumnInfo(name="name")
public String name;

@ColumnInfo(name="pversion")
    public String pversion;
@ColumnInfo(name="upicture")
public byte[] upicture;
    @PrimaryKey @NonNull
    public String uid;

    public User(String uid,
            String name,
                byte[] upicture, String pversion ){
        this.uid=uid;
        this.name=name;
        this.upicture=upicture;
        this.pversion=pversion;
    }
    public String get_uid(){
        return uid;
    }
    public String get_name(){
        return name;
    }
    public String get_pversion(){
        return pversion;
    }
    public byte[] get_upicture(){
        return upicture;
    }
}

My Datbase DAO:

@Dao
public interface UserDAO {

    @Query("select Exists(select uid from User where uid =:useruid)")
    Boolean loadAllByuid(String useruid);
    @Query("select*from User")
    List<User> getAll();
    @Insert
    void insertAll(User...users);
}

Appdatabase DAO:

@Database(entities = {User.class},version=1)
public abstract  class AppDatabase extends RoomDatabase {
    public abstract UserDAO userDAO();
}

In model class:

public class Model_user {
    private static Model_user theinstance = null;
    private ArrayList<User> user_list;
    private static AppDatabase userDAO = null;
 
    public static synchronized Model_user getInstance() {
        if (theinstance == null) {
            theinstance = new Model_user();
        }
        return theinstance;
    }

    public static synchronized Model_user getInstance(Context c) {
        if (theinstance == null) {
            userDAO = Room.databaseBuilder(c, AppDatabase.class, "userdb").build();
            theinstance = new Model_user();
        }
        return theinstance;
    }
    public void addUser(User[] s) throws Exception {
        Log.d("main_activity_uid","ok sta partendo");
        userDAO.userDAO().insertAll(s);
        user_list.addAll(Arrays.asList(s));
        Log.d("main_activity_uidd","ok hai inserito crrettamente");
        return;
    }

 public Boolean getUsersDBfromuid(String uid) {
       return userDAO.userDAO().loadAllByuid(sid);
    }
    
    public ArrayList<User> getUsers() {
        if (user_list.size() == 0) {
            user_list.addAll(userDAO.userDAO().getAll());
        }
        return user_list;
    }
   
    public void getUsersDB() {
        user_list.addAll(userDAO.userDAO().getAll());
    }

    public int getsize() {
        return Model_user.getInstance().getUsers().size();
    }

Now in my code i cannot enter data and query the database DAO.My code is:

new Thread((new Runnable() {
            @Override
            public void run() {
                try {
                    Model_user.getInstance
                            (activity.getApplicationContext()).addUser(user.toArray(new User[0]));
                    Log.d("main_activitytt",String.valueOf(Model_user.getInstance
                            (activity.getApplicationContext()).
                            getUsersDBfromuid("hello")));
                } catch (JSONException e) {
                    e.printStackTrace();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        })).start();

why can't I enter data and query the database? where am I wrong? Furthermore, the LOG does not print true or false

Answer 1

Have you checked your code . There is error in your code ?

public Boolean getUsersDBfromuid(String uid) {
    return userDAO.userDAO().loadAllByuid(sid);
}

sid shouldbe replaced by uid .