会议室数据库-无法从数据库中获取数据子集

Question

我知道可以从数据库中获取表中的所有数据，但是我无法获得一种使用外键筛选数据的有效方法。我将如何实现其中的Java部分？

我要做的是在RecyclerView中显示分配给选定术语的所有课程。

    /*
     * Returns the list of courses assigned to the selected term
     */
    RecyclerView recyclerView = findViewById(R.id.term_courses_added_recyclerview);
    recyclerView.setLayoutManager(new LinearLayoutManager(this));
    recyclerView.setHasFixedSize(true);

    AssignCourseAdapter adapter = new AssignCourseAdapter();
    recyclerView.setAdapter(adapter);

//        courseViewModel = ViewModelProviders.of(this).get(CourseViewModel.class);
//        courseViewModel.getCoursesById().observe(this, new Observer<List<TermEntity>>() {
//            @Override
//            public void onChanged(List<TermEntity> termEntities) {
//                adapter.setTerms(termEntities);
//            }
//        });

CourseDao：

@Dao 
public interface CourseDao {

/**
 * Insertion queries
 * insertCourse inserts one course
 * insertAll inserts all courses entered - not implemented
 */
@Insert(onConflict = OnConflictStrategy.REPLACE)
void insertCourse(CourseEntity course);

@Insert(onConflict = OnConflictStrategy.REPLACE)
void insertAll(List<CourseEntity> courses);

/**
 * Update queries
 * updateCourse updates the currently selected course
 */
@Update(onConflict = OnConflictStrategy.REPLACE)
void updateCourse(CourseEntity course);

/**
 * Deletion queries
 * deleteCourse deletes the currently selected course
 * deleteAll deletes all courses in the table
 */
@Delete
void deleteCourse(CourseEntity course);

@Query("DELETE FROM courses")
void deleteAllCourses();

/**
 * Return queries
 * getAll returns all courses ordered by name
 * getCourseById returns a course that matches the selected course id
 * getCoursesByTerm returns all courses that match the selected term id
 */
@Query("SELECT * FROM courses ORDER BY courseStartDate DESC")
LiveData<List<CourseEntity>> getAllCourses();

@Query("SELECT * FROM courses WHERE courseId = :courseId")
LiveData<List<CourseEntity>> getCourseById(int courseId);

@Query("SELECT * FROM courses WHERE termId = :termId")
LiveData<List<CourseEntity>> getCoursesByTerm(final int termId);
}

应用程序存储库课程代码：

    /*
 * Course Queries
 */
public void insertCourse(CourseEntity course) {
    new InsertCourseAsyncTask(courseDao).execute(course);
}

private static class InsertCourseAsyncTask extends AsyncTask<CourseEntity, Void, Void> {
    private CourseDao courseDao;

    private InsertCourseAsyncTask(CourseDao courseDao) {
        this.courseDao = courseDao;
    }

    @Override
    protected Void doInBackground(CourseEntity... courseEntities) {
        courseDao.insertCourse(courseEntities[0]);
        return null;
    }
}

public void updateCourse(CourseEntity course) {
    new UpdateCourseAsyncTask(courseDao).execute(course);
}

private static class UpdateCourseAsyncTask extends AsyncTask<CourseEntity, Void, Void> {
    private CourseDao courseDao;

    private UpdateCourseAsyncTask(CourseDao courseDao) {
        this.courseDao = courseDao;
    }

    @Override
    protected Void doInBackground(CourseEntity... courseEntities) {
        courseDao.updateCourse(courseEntities[0]);
        return null;
    }
}

public void deleteCourse(CourseEntity course) {
    new DeleteCourseAsyncTask(courseDao).execute(course);
}

private static class DeleteCourseAsyncTask extends AsyncTask<CourseEntity, Void, Void> {
    private CourseDao courseDao;

    private DeleteCourseAsyncTask(CourseDao courseDao) {
        this.courseDao = courseDao;
    }

    @Override
    protected Void doInBackground(CourseEntity... courseEntities) {
        courseDao.deleteCourse(courseEntities[0]);
        return null;
    }
}

public void deleteAllCourses() {
    new DeleteAllCoursesAsyncTask(courseDao).execute();
}

private static class DeleteAllCoursesAsyncTask extends AsyncTask<Void, Void, Void> {
    private CourseDao courseDao;

    private DeleteAllCoursesAsyncTask(CourseDao courseDao) {
        this.courseDao = courseDao;
    }

    @Override
    protected Void doInBackground(Void... voids) {
        courseDao.deleteAllCourses();
        return null;
    }
}

public LiveData<List<CourseEntity>> getAllCourses() {
    return allCourses;
}

public LiveData<List<CourseEntity>> getAllAssignedCourses(final int termId) {
    return courseDao.getCoursesByTerm(termId);
}

CourseViewModel：

public class CourseViewModel extends AndroidViewModel {
private AppRepository repository;
private LiveData<List<CourseEntity>> allCourses;
private LiveData<List<CourseEntity>> allAssignedCourses;

public CourseViewModel(@NonNull Application application) {
    super(application);
    repository = new AppRepository(application);
    allCourses = repository.getAllCourses();
    //allAssignedCourses = repository.getAllAssignedCourses(termId);
}

public void insertCourse(CourseEntity course) {
    repository.insertCourse(course);
}

public void updateCourse(CourseEntity course) {
    repository.updateCourse(course);
}

public void deleteCourse(CourseEntity course) {
    repository.deleteCourse(course);
}

public void deleteAllCourses() {
    repository.deleteAllCourses();
}

public LiveData<List<CourseEntity>> getAllCourses() {
    return allCourses;
}
//    public LiveData<List<CourseEntity>> getAllAssignedCourses(final int termId) {
//        return allAssignedCourses;
//    }
}