java - 如何使用 Rxjava 预填充 android 房间数据库

Question

如何使用 Rxjava 正确预填充我的数据库

这是我的道

@Query("SELECT * from questions WHERE difficulty  = :difficulty")
Flowable<List<Question>> getQuestions(String difficulty);

// Emits the number of users added to the database.
@Insert
public Maybe<long[]> insertQuestions(List<Question> questions);

这是我的数据库类

    public static synchronized QuestionDatabase getInstance(Context context) {
    if (instance == null) {
        instance = Room.databaseBuilder(context.getApplicationContext(), QuestionDatabase.class, "questions_database")
                .fallbackToDestructiveMigration()
                //.addMigrations(MIGRATION_1_2)
                .addCallback(roomCallback)
                .build();
    }
    return instance;
}

private static RoomDatabase.Callback roomCallback = new RoomDatabase.Callback() {
    @Override
    public void onCreate(@NonNull SupportSQLiteDatabase db) {
        super.onCreate(db);

        QuestionDao questionDao = instance.questionDao();

        List<Question> questions = new ArrayList<>();

        questions.add(new Question("A is correct", "A", "B", "C", 1, GameConstants.DIFFICULTY_EASY));
        questions.add(new Question("C is correct", "A", "B", "C", 3, GameConstants.DIFFICULTY_HARD));
        questions.add(new Question("B is correct", "A", "B", "C", 2, GameConstants.DIFFICULTY_EASY));

        //inserting records
        questionDao.insertQuestions(questions)
                .subscribeOn(Schedulers.io())
                //.observeOn(AndroidSchedulers.mainThread())
                .subscribe(
                        new Consumer<long[]>() {

                            @Override
                            public void accept(long[] longs) throws Exception {

                            }
                        },
                        new Consumer<Throwable>() {
                            @Override
                            public void accept(Throwable throwable) throws Exception {

                            }
                        });


    }
};

我遇到的问题如下：

仅当我在活动 p.Ex 上调用方法时才会填充数据库：

        //getting flowable to subscribe consumer that will access the data from Room database.
    questionDao.getQuestions(GameConstants.DIFFICULTY_HARD)
            .subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe(
            new Consumer<List<Question>>() {
                @Override
                public void accept(List<Question> questions) throws Exception {

                    questionList = (ArrayList<Question>)questions;
                    questionCountTotal = questionList.size();
                    Collections.shuffle(questionList);
                    showNextQuestion();
                }
            },
            new Consumer<Throwable>() {
                @Override
                public void accept(Throwable throwable) throws Exception {

                }
            }
    );

当我调用这个方法时，我得到了两次问题。我通过在 questionDao.getQuestions 的接受方法中放置一个断点来检查这一点。我相信有两个线程正在运行，一个用于填充，另一个用于获取问题。

为什么会发生这种情况，我该如何以正确的方式实现它？

提前致谢

标签： javaandroidrx-java2android-roompopulate

Answer 1

我相信以下更改将起作用

1. 更改getInstance方法以强制打开数据库，从而导致onCreate在您获取实例时运行，而不是在您尝试访问数据库之前运行。

根据（见评论）： -

public static synchronized QuestionDatabase getInstance(Context context) {
    if (instance == null) {
        instance = Room.databaseBuilder(context.getApplicationContext(), QuestionDatabase.class, "questions_database")
                .fallbackToDestructiveMigration()
                //.addMigrations(MIGRATION_1_2)
                .addCallback(roomCallback)
                .build();
    }
    instance.getOpenHelper().getWritableDatabase(); //<<<<<<<<<< Forces an Open thus creation of the Database
    return instance;
}

2. 添加初始问题而不订阅

即代替

    //inserting records
    questionDao.insertQuestions(questions)
            .subscribeOn(Schedulers.io())
            //.observeOn(AndroidSchedulers.mainThread())
            .subscribe(
                    new Consumer<long[]>() {

                        @Override
                        public void accept(long[] longs) throws Exception {

                        }
                    },
                    new Consumer<Throwable>() {
                        @Override
                        public void accept(Throwable throwable) throws Exception {

                        }
                    });

只需使用：-

    questionDao.insertQuestions(questions);

当您在活动中恢复实例时，将填充数据库。