Get user by userId in ROOM-CodePudding

I want to take event by id but it returns unit.

Entity:

@Dao
interface EventDao {
    @Query("SELECT * FROM event_table WHERE eventId= :myeventId")
    fun getEventByEventId(myeventId: Int): LiveData<Event>
}

Repository:

class EventRepository(private val eventDao: EventDao){
    fun getEventById(myeventId: Int): LiveData<Event>{
            return eventDao.getEventByEventId(myeventId = myeventId)
    }
}

Viewmodel:

class EventViewModel (application: Application): AndroidViewModel(application) {
 private val readEventById = MutableLiveData<LiveData<Event>>()
fun getEventById(eventId: Int) {
        viewModelScope.launch(Dispatchers.IO) {
            readEventById.postValue(eventRepository.getEventById(eventId))
        }
    }
}

I am calling it on user fragment:

lifecycleScope.launch {
        val event = eventViewModel.getEventById(currentUserId)
    }

but it returns unit. How can i return event by userId?

CodePudding user response：

try this

suspend fun getEventById(eventId: Int): LiveData<Event> {
    return withContext(Dispatchers.IO) {
        eventRepository.getEventById(eventId)
    }
}

CodePudding user response：

In your ViewModel class, you should include a public LiveData<Event> value that returns the readEventById live data object:

val selectedEvent: LiveData<Event>
    get() = readEventById

Then, in the user Fragment, you should instead add an Observer on eventViewModel.selectedEvent. When you call eventViewModel.getEventById(currentUserId), you don't worry about the result. Instead, the Observer will let you know the LiveData<Event> was updated and you can handle the value this way.

This is the proper approach since you're getting the data from the database asynchronously.