A Hilt module providing a Room database using a RoomDatabase.Callback

DatabaseModule.kt

@InstallIn(SingletonComponent::class)
@Module
object DatabaseModule {
    @Singleton
    @Provides
    fun provideTeaDao(database: AppDatabase):TeaDao = database.teaDao()

    @Provides
    @Singleton
    fun provideDatabase(
        @ApplicationContext appContext: Context,
        /*
        This is kind of cool.. You can't pass in teaDao directly, bc that
        would be a circular dependency.  By passing the Provider, you can
        call its get() method _after_ .build() has been executed, i.e. in the
        callback.  I guess Hilt knows how to inject the Provider from the
        provideTeaDao function above.
         */
         provider: Provider<TeaDao>
        ): AppDatabase {
        return Room.databaseBuilder(
            appContext,
            AppDatabase::class.java,
            "app_database")
            .addCallback(StartingTeas(appContext, provider))
            .build()
    }
}