android room suspend insert success but does not return id

Question

I'm trying to use room database with suspend keyword.

I can successfully insert a data into database. But after that, the insert method will not return anything, that means I can't do anything after insertion such as insert another data by the returned id.

here is my sample code:

@Dao
interface EventDao {
    ...

    @Insert
    suspend fun insert(event: Event): Long

    ...
}

class EventRepository(...) {
    ...

    suspend fun insertEvent(event: Event, personId: Long) {
        val id = eventDao.insertSync(event)

        // !!! FREEZE - the code below here will never reach !!!

        val attendee = EventAttendee(
            personId = personId,
            eventId = id
        )
        eventAttendeeDao.insert(attendee)
    }

    ...
}

class EventEditingViewModel(...) : ViewModel() {
    ...

    fun addEvent(event: Event) {
        event.userId = userId
        viewModelScope.launch {
            eventRepository.insertEvent(event, friendId)
        }
    }

    ...
}

Actually, if I remove suspend keyword, I can get the return id properly. The freezing problem will only happen when I use suspend keyword in front of insertion method in Dao class.

Logcat doesn't show any logs of this, and the app doesn't crash, so I have no idea what happened.

My room version is 2.2.1. and I've tried 2.2.2 also.

Did I do the wrong way to use suspend function in room database?

Morshues Morshues · Accepted Answer · 2019-12-05T08:32:04

I looked into coroutines library then found out that my insert method has been canceled cause by ViewModel deleted.

Because I built a DialogFragment and do the insertion after I click the PositiveButton of AlertDialog, so the viewModelScope has been clear before the insertion finished.

I think the solution may be the following ways:

use another scope such as GlobalScope.launch instead of viewModelScope.launch
dismiss the dialog after insertion.
return the data to another fragment, do the insertion in another page.

In this case, I think the best choice is the first choice. It's easier and would not cause any other lifecycles' problem.

android room suspend insert success but does not return id

2 Answers