Is there any way to pass a Flow into a Room DAO Query method?

user_1015126 0
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I'm working on implementing Room in an android app and I have a use case where I am receiving a Flow with the current user id for functionality similar to switching which logged in Google user to view a service as. I'd like to pass that flow into a @Query annotated method in my DAO to get user widgets so that if the currently selected user changes or the list of widgets stored changes, the output Flow<List> would change as well.

Something like

WidgetRepo.kt

val widgets: Flow<List<Widget>> = widgetDAO.getWidgetsByUser(currentUserID)

WidgetDao.kt

@Query("select * from widget where userID = :userID")
fun getWidgetsByUser(userID: Flow<Int>): Flow<List<Widget>>
android-room kotlin-coroutines kotlin android
2 Answers

I don't think that's a good practice. I would rather do the following logic in a specific use-case, for example:

class GetWidgetsByUserUseCase(
    private val userRepo: UserRepository,
    private val widgetLocalSource: WidgetRepository
){

    suspend operator fun invoke() = userRepo.flatMapLatest { user ->
            widgetLocalSource.getWidgetsByUser(user.id)
        }

}

With this implementation every time a new user is emitted, the widgetLocalSource.getWidgetsByUser() will be triggered and the previous flows will be canceled.

See flatMapLatest for more information on the operator.

user_44878580

Room Database has supported Flow since before. Add this to gradle:

 // Kotlin Extensions and Coroutines support for Room - latest Room version 2.3.0
 implementation("androidx.room:room-ktx:$room_version")

See more Write observable queries with Room here.

Admin1
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