java.lang.IllegalStateException when collecting flow from SqlDelight in ViewModel

Question

I am trying to use SqlDelight database in my app.

In my DAO, I have a function called getRecipeById to query the database and return a flow of domain model (Recipe). Here is the implementation of the function: (Note: RecipeTable is the name of the table, or I guess I should have called it RecipeEntity)

fun getRecipeById(id: Int): Flow<Recipe> {
    return recipeQueries.getRecipeById(id)
        .asFlow()
        .mapToOne()
        .map { recipeTable: RecipeTable ->
            recipeTableToRecipeMapper(recipeTable = recipeTable)
        }
}

Then my repository calls this function like this: (Note: recipeLocalDatabase is my DAO)

suspend fun getRecipeById(id: Int): Flow<RecipeDTO> {
    val recipeFromDB: Flow<Recipe> = recipeLocalDatabase.getRecipeById(id)
    return recipeFromDB.map { recipe: Recipe ->
        recipeDTOMapper.mapDomainModelToDTO(recipe)
    }
}

Then my usecase layer calls the function from repository and pass along the flow:

suspend fun execute(
    id: Int
): UseCaseResult<Flow<RecipeDTO>>
{
    return try{
        UseCaseResult.Success(recipeRepository.getRecipeById(id))
    } catch(exception: Exception){
        UseCaseResult.Error(exception)
    }
}

Now within the ViewModel, I am collecting the flow of RecipeDTO like this:

var recipeForDetailView: MutableState<RecipeDTO> = mutableStateOf(
    RecipeDTO(
        id  = 0,
        title = "",
        featuredImage = "",
        ingredients = listOf()
    )
)

fun onLaunch(recipeId: Int){
    viewModelScope.launch(Dispatchers.IO) {
        when(val result = getRecipeDetailUseCase.execute(recipeId))
        {
            is UseCaseResult.Success ->
                 result.resultValue.collect{ recipeDTO: RecipeDTO ->
                     recipeForDetailView.value = recipeDTO
                 }
            is UseCaseResult.Error -> Log.d("Debug: RecipeDetailViewModel",
                result.exception.toString()
            )
        }
    }
}

My View layer will then observe the MutableState object. Now, I keep getting this error every once a while

E/AndroidRuntime: FATAL EXCEPTION: DefaultDispatcher-worker-5
Process: com.noat.recipe_food2fork, PID: 13923
java.lang.IllegalStateException: Reading a state that was created after the snapshot was taken or in a snapshot that has not yet been applied
    at androidx.compose.runtime.snapshots.SnapshotKt.readError(Snapshot.kt:1530)
    at androidx.compose.runtime.snapshots.SnapshotKt.current(Snapshot.kt:1770)
    at androidx.compose.runtime.SnapshotMutableStateImpl.setValue(SnapshotState.kt:891)
    at com.noat.recipe_food2fork.ui.viewModel.RecipeDetailViewModel$onLaunch$1$invokeSuspend$$inlined$collect$1.emit(Collect.kt:133)
    at com.noat.recipe_food2fork.data.repositoryImplementation.recipeRepository.RecipeRepository$getRecipeById$$inlined$map$1$2.emit(Collect.kt:135)
    at com.noat.recipe_food2fork.data.local.RecipeLocalDatabase$getRecipeById$$inlined$map$1$2.emit(Collect.kt:135)
    at com.squareup.sqldelight.runtime.coroutines.FlowQuery$mapToOne$$inlined$map$1$2.emit(Collect.kt:135)
    at com.squareup.sqldelight.runtime.coroutines.FlowQuery$mapToOne$$inlined$map$1$2$1.invokeSuspend(Unknown Source:12)
    at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
    at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
    at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:571)
    at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:750)
    at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:678)
    at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:665)

I think it is the flow collecting that caused the error, or maybe because of the fact that I am using MutableState? Googling the error does not help much... Does anyone know what is the cause of this issue? Thank you! Sorry for the long long post.

Answer 1

I don't think MutableState is designed to be used in the ViewModel layer, since it's an observable integrated with the compose runtime. You could create a MutableStateFlow instead and use collectAsState() from the view layer.

In your case the issue is probably, because of the state is captured in a coroutine invoked outside composition.