如果我想查询特定的with Room，我应该如何编码？

Question

我现在正在学习如何使用Android中的Room在本地数据库中保存数据。我已经在这个链接中完成了Codelab。https://developer.android.com/codelabs/android-room-with-a-view#0我可以更新、插入、删除和查询表中的所有数据。现在，我希望使用特定的id查询数据。我应该如何在ViewModel和Repository类中编码？谢谢。我的桌子名叫“日记”，Diary.class

@Entity(tableName = "diary_table")
public class Diary {

    @PrimaryKey(autoGenerate = true)
    private int id;

    @ColumnInfo(name = "diary_title")
    private String diary_Title;
    @ColumnInfo(name = "diary_content")
    private String diary_Content;


    public Diary(@NonNull String diary_Title, String diary_Content) {
        this.diary_Title = diary_Title;
        this.diary_Content = diary_Content;
    }
    
    public void setDiary_Title(String diary_Title) {
        this.diary_Title = diary_Title;
    }

    public void setDiary_Content(String diary_Content) {
        this.diary_Content = diary_Content;
    }

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

    public int getId() {
        return id;
    }

    public String getStrId() {
        return String.valueOf(id);
    }

    public String getDiary_Title() {
        return diary_Title;
    }

    public String getDiary_Content() {
        return diary_Content;
    }
}

DiaryDao.class

@Dao
public interface DiaryDao {

    @Insert
    void insertDiaries(Diary... diaries);

    @Update
    void updateDiaries(Diary... diaries);

    @Delete
    void deleteDiaries(Diary... diaries);

    //删除到一无所有 慎用！
    @Query("DELETE FROM diary_table")
    void deleteAllDiaries();

    @Query("SELECT * FROM diary_table ORDER BY ID ASC")
    LiveData<List<Diary>>getAllDiariesLive();//get all diary

    @Query("SELECT * FROM diary_table WHERE ID=:id")
    LiveData<Diary> getSpecificDiariesLive(int id);//get specific diary

}

DiaryRepository

class DiaryRepository {
    private LiveData<Diary> specificDiary;
    private LiveData<List<Diary>> allDiariesLive;
    private DiaryDao diaryDao;

    DiaryRepository(Context context) {
        DiaryRoomDatabase diaryRoomDatabase = DiaryRoomDatabase.getDiaryDatabase(context.getApplicationContext());
        diaryDao = diaryRoomDatabase.getDiaryDao();
        allDiariesLive = diaryDao.getAllDiariesLive();
        specificDiary = diaryDao.getSpecificDiariesLive(/**how should i code here***/);
    }

    void insetDiaries(Diary... diaries) {
        new InsertAsyncTask(diaryDao).execute(diaries);
    }

    void updateDiaries(Diary... diaries) {
        new UpdateAsyncTask(diaryDao).execute(diaries);
    }

    void deleteDiaries(Diary... diaries) {
        new DeleteAsyncTask(diaryDao).execute(diaries);
    }

    void deleteAllDiaries(Diary... diaries) {
        new DeleteAllAsyncTask(diaryDao).execute();
    }

    LiveData<Diary> getSpecificDiary(int i) {return specificDiary; }

    LiveData<List<Diary>> getAllDiariesLive() {
        return allDiariesLive;
    }

    static class InsertAsyncTask extends AsyncTask<Diary, Void, Void> {
        private DiaryDao diaryDao;

        InsertAsyncTask(DiaryDao diaryDao) {
            this.diaryDao = diaryDao;
        }


        @Override
        protected Void doInBackground(Diary... diaries) {
            diaryDao.insertDiaries(diaries);
            return null;
        }
    }

    static class UpdateAsyncTask extends AsyncTask<Diary, Void, Void> {
        private DiaryDao diaryDao;

        UpdateAsyncTask(DiaryDao diaryDao) {
            this.diaryDao = diaryDao;
        }

        @Override
        protected Void doInBackground(Diary... diaries) {
            diaryDao.updateDiaries(diaries);
            return null;
        }
    }

    static class DeleteAsyncTask extends AsyncTask<Diary, Void, Void> {
        private DiaryDao diaryDao;

        DeleteAsyncTask(DiaryDao diaryDao) {
            this.diaryDao = diaryDao;
        }

        @Override
        protected Void doInBackground(Diary... diaries) {
            diaryDao.deleteDiaries(diaries);
            return null;
        }

    }

    static class DeleteAllAsyncTask extends AsyncTask<Void, Void, Void> {
        private DiaryDao diaryDao;

        DeleteAllAsyncTask(DiaryDao diaryDao) {
            this.diaryDao = diaryDao;
        }

        @Override
        protected Void doInBackground(Void... voids) {
            diaryDao.deleteAllDiaries();
            return null;
        }

    }
}

DiaryViewModel.class

public class DiaryViewModel extends AndroidViewModel {
    private DiaryRepository diaryRepository;

    public DiaryViewModel(@NonNull Application application) {
        super(application);
        diaryRepository = new DiaryRepository(application);
    }

    public LiveData<Diary> getSpecificDiary(/**how should i code here?**/) {
        return diaryRepository.getSpecificDiary(i);
    }

    public LiveData<List<Diary>> getAllDiariesLive() {
        return diaryRepository.getAllDiariesLive();
    }

    public void insertDiaries(Diary... diaries) {
        diaryRepository.insetDiaries(diaries);
    }

    public void updateDiaries(Diary... diaries) { diaryRepository.updateDiaries(diaries); }

    public void deleteDiary(Diary... diaries) { diaryRepository.deleteDiaries(diaries);}

    public void deleteAllDiaries() {
        diaryRepository.deleteAllDiaries();
    }
}

Answer 1

我认为在DiaryRepository：

class DiaryRepository {
private LiveData<List<Diary>> allDiariesLive;
private DiaryDao diaryDao;

DiaryRepository(Context context) {
    DDiaryRoomDatabase diaryRoomDatabase = DiaryRoomDatabase.getDiaryDatabase(context.getApplicationContext());
    diaryDao = diaryRoomDatabase.getDiaryDao();
    allDiariesLive = diaryDao.getAllDiariesLive();
}


void insetDiaries(Diary... diaries) {
    new InsertAsyncTask(diaryDao).execute(diaries);
}

void updateDiaries(Diary... diaries) {
    new UpdateAsyncTask(diaryDao).execute(diaries);
}

void deleteDiaries(Diary... diaries) {
    new DeleteAsyncTask(diaryDao).execute(diaries);
}

void deleteAllDiaries(Diary... diaries) {
    new DeleteAllAsyncTask(diaryDao).execute();
}

LiveData<Diary> getSpecificDiary(int i) {
    return diaryDao.getSpecificDiariesLive(i); 
}

LiveData<List<Diary>> getAllDiariesLive() {
    return allDiariesLive;
}

...

因此，您的ViewModel将更改为：

public class DiaryViewModel extends AndroidViewModel {
private DiaryRepository diaryRepository;

public DiaryViewModel(@NonNull Application application) {
    super(application);
    diaryRepository = new DiaryRepository(application);
}

public LiveData<Diary> getSpecificDiary(int i) {
    return diaryRepository.getSpecificDiary(i);
}
...

Answer 2

DiaryRepository.class和ViewModel.class喜欢hosseini sajad代码。我应该在livedata中使用它，如下所示：

mDiaryViewModel = new ViewModelProvider(activity).get(DiaryViewModel.class);
mDiaryViewModel.getSpecificDiary(pos+1).observe(activity, diary -> {
                    Log.d("test", "Here is the Title: " + diary.getDiary_Title() + "\n" + "Here is the Content: " +diary.getDiary_Content() );
                });