Android Room - Trying to query a single row based on Primary ID-CodePudding

What am I trying to achieve ?

Get a single row of data which has the id I need. The SQL equivalent of SELECT * FROM favs WHERE link='link'. I have written a fun named getOneFav() which for this. I am following the tutorial https://developer.android.com/codelabs/android-room-with-a-view-kotlin#0 and code from https://github.com/android/sunflower

What have I setup so far ?

Entity

@Entity(tableName = "favs")
data class Favorite(
    @PrimaryKey @ColumnInfo(name = "link") val link : String,
    @ColumnInfo(name = "keywords") val keywords : String
)

DAO

@Dao
interface FavDAO {
    @Query("SELECT * FROM favs")
    fun getAllFavsLive(): Flow<List<Favorite>>

    @Query("SELECT * FROM favs WHERE link = :link")
    fun getOneFav(link: String): Favorite

    @Insert(onConflict = OnConflictStrategy.IGNORE)
    suspend fun insert(link: Favorite)
}

Repository

class FavRepo (private val favDao: FavDAO) {

    val allFavs: Flow<List<Favorite>> = favDao.getAllFavsLive()

    @Suppress("RedundantSuspendModifier")
    @WorkerThread
    suspend fun insert(link: Favorite) {
        favDao.insert(link)
    }

    fun getOneFav(link: String) = favDao.getOneFav(link)

    @Suppress("RedundantSuspendModifier")
    @WorkerThread
    suspend fun delete(link: String) {
        favDao.delete(link)
    }
}

ViewModel

class FavViewModel (private val repository: FavRepo) : ViewModel() {

    val allFavs: LiveData<List<Favorite>> = repository.allFavs.asLiveData()

    fun insert(link: Favorite) = viewModelScope.launch {
        repository.insert(link)
    }

    fun getOneFav(link: String) = repository.getOneFav(link)

}

class FavViewModelFactory(private val repository: FavRepo) : ViewModelProvider.Factory {
    override fun <T : ViewModel> create(modelClass: Class<T>): T {
        if (modelClass.isAssignableFrom(FavViewModel::class.java)) {
            @Suppress("UNCHECKED_CAST")
            return FavViewModel(repository) as T
        }
        throw IllegalArgumentException("Unknown ViewModel class")
    }
}

What problems am I facing ?

I am receiving an error saying

java.lang.RuntimeException: Unable to start activity ComponentInfo{[package name removed].MainActivity}: java.lang.IllegalStateException: Cannot access database on the main thread since it may potentially lock the UI for a long period of time.

What have I tried so far ?

I have tried -

Adding suspend in front of the function getOneFav in DAO and Repository
Made the function run inside viewModelScope. It gave the same error as above. Also, this way the function returned a Job instead of the 'Favorite' data class object.

    fun getOneFav(link: String) = viewModelScope.launch {
        repository.getOneFav(link)
    }

Followed this method here - How to implement a Room LiveData filter which even though worked, which seemed like an overkill for something so simple. Also despite the fact that the code is using MutableLiveData, I wasn't able to see any triggers when the insert happened.

CodePudding user response：

in your Db try adding .fallbackToDestructiveMigration().allowMainThreadQueries().build() after the room database builder to put that ANR check

CodePudding user response：

You should run your queries in a different context:

class FavRepo (private val favDao: FavDAO) {

    val allFavs: Flow<List<Favorite>> = withContext(Dispatchers.IO) { 
        favDao.getAllFavsLive()
    }

    @Suppress("RedundantSuspendModifier")
    @WorkerThread
    suspend fun insert(link: Favorite) = withContext(Dispatchers.IO) {
        favDao.insert(link)
    }

    fun getOneFav(link: String) = withContext(Dispatchers.IO) { 
        favDao.getOneFav(link)
    }

    @Suppress("RedundantSuspendModifier")
    @WorkerThread
    suspend fun delete(link: String) = withContext(Dispatchers.IO) {
        favDao.delete(link)
    }
}