Android Room - 获取新插入行表单的 id @Insert

Question

In my code below I'm getting rowId . I've read that it's also possible to get the last inserted row id from @Insert directly. In my code I changed void insert to long and tried many other things as in examples I found on the internet, but every time I get errors. Would you like to provide me a code/solution to get the row/user ID from @Insert?

@Dao
public interface UserDao {

    @Insert
    void insert(UserEntity userEntity);

    @Update
    void update(UserEntity userEntity);

    @Delete
    void delete(UserEntity userEntity);

    @Query("DELETE FROM user_table")
    void deleteAllUsers();

    @Query("SELECT * FROM user_table")
    LiveData<List<UserEntity>> getAllUsers();

//    ====== from here ======

    @Query("SELECT * FROM user_table")
    LiveData<UserEntity> getRowId();

//    ====== till here ======

}

Entity

@Entity(tableName = "user_table")
public class UserEntity {

    @PrimaryKey(autoGenerate = true)
    private int id;

    private String userName;

    private String userTelephoneNumber;

    public UserEntity(String userName, String userTelephoneNumber) {
        this.userName = userName;
        this.userTelephoneNumber = userTelephoneNumber;
    }

    public void setId(int id) {
        this.id = id;
    }

    public int getId() {
        return id;
    }

    public String getUserName() {
        return userName;
    }

    public String getUserTelephoneNumber() {
        return userTelephoneNumber;
    }
}

Repository

public class UserRepository {
    private UserDao userDao;
    private LiveData<List<UserEntity>> allUsers;

    public UserRepository(Application application) {
        HandymanDatabase handymanDatabase = HandymanDatabase.getInstance(application);
        userDao = handymanDatabase.userDao();
        allUsers = userDao.getAllUsers();
    }

    public void insert(UserEntity userEntity) {
        new InsertUserAsyncTask(userDao).execute(userEntity);
    }

    public void update(UserEntity userEntity) {
        new UpdateUserAsyncTask(userDao).execute(userEntity);
    }

    public void delete(UserEntity userEntity) {
        new DeleteUserAsyncTask(userDao).execute(userEntity);
    }

    public void deleteAllUsers() {
        new DeleteAllUsersAsyncTask(userDao).execute();
    }

    public LiveData<List<UserEntity>> getAllUsers() {
        return allUsers;
    }

//    ====== from here ======

    public LiveData<UserEntity> getRowId() {
        return userDao.getRowId();
    }

//    ====== till here ======


    private static class InsertUserAsyncTask extends AsyncTask<UserEntity, Void, Void> {
        private UserDao userDao;

        private InsertUserAsyncTask(UserDao userDao) {
            this.userDao = userDao;
        }

        @Override
        protected Void doInBackground(UserEntity... userEntities) {
            userDao.insert(userEntities[0]);
            return null;
        }
    }

    private static class UpdateUserAsyncTask extends AsyncTask<UserEntity, Void, Void> {
        private UserDao userDao;

        private UpdateUserAsyncTask(UserDao userDao) {
            this.userDao = userDao;
        }

        @Override
        protected Void doInBackground(UserEntity... userEntities) {
            userDao.update(userEntities[0]);
            return null;
        }
    }

    private static class DeleteUserAsyncTask extends AsyncTask<UserEntity, Void, Void> {
        private UserDao userDao;

        private DeleteUserAsyncTask(UserDao userDao) {
            this.userDao = userDao;
        }

        @Override
        protected Void doInBackground(UserEntity... userEntities) {
            userDao.delete(userEntities[0]);
            return null;
        }
    }

    private static class DeleteAllUsersAsyncTask extends AsyncTask<Void, Void, Void> {
        private UserDao userDao;

        private DeleteAllUsersAsyncTask(UserDao userDao) {
            this.userDao = userDao;
        }

        @Override
        protected Void doInBackground(Void... voids) {
            userDao.deleteAllUsers();
            return null;
        }
    }
}

ViewModel

public UserViewModel(@NonNull Application application) {
        super(application);
        userRepository = new UserRepository(application);
        allUsers = userRepository.getAllUsers();
    }

    public void insert(UserEntity userEntity) {
        userRepository.insert(userEntity);
    }

    public void update(UserEntity userEntity) {
        userRepository.update(userEntity);
    }

    public void delete(UserEntity userEntity) {
        userRepository.delete(userEntity);
    }

    public void deleteAllUsers() {
        userRepository.deleteAllUsers();
    }

    public LiveData<List<UserEntity>> getAllUsers() {
        return allUsers;
    }

//    ====== from here ======

    public LiveData<UserEntity> getRowId() {
        return userRepository.getRowId();
    }

//    ====== till here ======

}

Fragment/Activity

public class UserFavoritesFragment extends Fragment {

    private static final String TAG = "UserFavoritesFragment";

    private UserViewModel userViewModel;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        View view = getLayoutInflater().inflate(R.layout.fragment_user_favorites, container, false);

        final TextView textViewUserName = view.findViewById(R.id.textViewUserName);
        TextView textViewUserPhone = view.findViewById(R.id.textViewUserPhone);

        userViewModel = new ViewModelProvider(this).get(UserViewModel.class);

//    ====== from here ======

        userViewModel.getRowId().observe(getViewLifecycleOwner(), new Observer<UserEntity>() {
            @Override
            public void onChanged(UserEntity userEntity) {

                long rowId = userEntity.getId();

                Log.d(TAG, "onChanged: " + rowId);

            }
        });

//    ====== till here ======

        return view;
    }
}

Answer 1

You can do that using a listener interface that has a callback that accepts a long value of the inserted row id in the database.

Listener Interface

public interface NewIdListener {
    void onInsert(long id);
}

Dao

@Dao
public interface UserDao {

    @Insert
    long insert(UserEntity userEntity); // return id of the inserted userEntity
    
}

Repository

public class UserRepository {
    private Executor mExecutor = Executors.newSingleThreadExecutor();
    private UserDao userDao;
    ...
    
    public void insertUserEntity(final UserEntity entity, final NewIdListener listener) {
        mExecutor.execute(new Runnable() {
            @Override
            public void run() {
                listener.onInsert(userDao.insert(entity));
            }
        });
}
    

ViewModel

public void insertUserEntity(UserEntity entity, NewIdListener listener) {
    userRepository.insertUserEntity(entity, listener);
}       

Activity

userViewModel.insertUserEntity(new UserEntity("User Name", "12345678"), new NewIdListener() {
    @Override
    public void onInsert(final long id) {
        requireActivity().runOnUiThread(new Runnable() {
            @Override
            public void run() {
                Toast.makeText(requireActivity(), "Id: " + id, Toast.LENGTH_SHORT).show();
            }
        });
    }
});

Note : For background thread, I've used Executor instead of AsyncTask as AsyncTask is deprecated now.