简书链接:room数据库初始化细节
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Room

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AppDatabase database = AppDatabase.getInstance(this, new AppExecutors());
         TemplateDao templeteDao = database.templeteDao();
         List<PrintTemplate> printTemplates = templeteDao.queryTemplateByField("title", "Box");//不查询就不触发自动，真贱
         Log.w(TAG,"PrintTemplate:"+printTemplates);//这里不能关闭数据库，否则将无法正常初始化。

如果在application的初始化中直接close,那么也会导致初始化失败，初始化的地方是回调。

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private static AppDatabase buildDatabase(final Context appContext,
           final AppExecutors executors) {
       return Room.databaseBuilder(appContext, AppDatabase.class, DATABASE_NAME)
               .allowMainThreadQueries()//允许主线程查询
               .setJournalMode(JournalMode.WRITE_AHEAD_LOGGING)
               .addCallback(new Callback() {
                   @Override
                   public void onCreate(@NonNull SupportSQLiteDatabase db) {
                       super.onCreate(db);
                       executors.diskIO().execute(() -> {
                           // Add a delay to simulate a long-running operation 添加延迟以模拟长时间运行的操作

                           if(BuildConfig.DEBUG){
                               Log.w("Appdatabase","DATABASE_INIT");
                           }
                           // Generate the data for pre-population 生成预人口数据
                           AppDatabase database = AppDatabase.getInstance(appContext, executors);
                           List<PrintTemplate> templeteEntries = DataGenerator.generateTempletes();
                           insertData(database, templeteEntries);
                           // notify that the database was created and it's ready to be used MutableLiveData flag=true
                           database.setDatabaseCreated();

                       });
                   }
               })
           .addMigrations(MIGRATION_1_2)//迁移
           .build();
   }

如上可以看到是在

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.addCallback(new Callback() {
                   @Override
                   public void onCreate(@NonNull SupportSQLiteDatabase db) {

里面触发的，但是关闭就会导致初始化基本上失败的，关闭了还不影响我查询操作，但是初始化失败的，关于该不该关闭的问题网上也有各种说法，