Android ROOM LIVEDATA not emitting the results

Question

Hi i have a list of items that i retrieve from a data source and then i apply a map on the observable to store the data into ROOM.

It manages to add it to the table but when i try to retrieve a LiveData of it, It doesnt seem to notify my observer of the results.

There is definetly data in the table and my query works as i changed the return time from LiveData to simple a List and that worked perfectly fine

Here is my data class

@Entity
data class Item(
        @PrimaryKey
        val id:String,
        val title: String,
        val description: String,
        val imgUrl: String,
        val  usageRules : List<String>,

)

Here is my DAO that exposes a func that add all the list of Items

@Dao
interface MyDao {

@Insert(onConflict = OnConflictStrategy.IGNORE)
    fun saveAllItems(itemList: MutableList<Item>)

       @Query("SELECT * FROM items")
    fun getAllItems(): LiveData<MutableList<Item>>

}

My DB class

@Database(entities = arrayOf(Item::class), version = 1, exportSchema = false)
@TypeConverters(UsageRulesTypeConverter::class)
abstract class MyDatabase : RoomDatabase() {
    abstract fun getProductDao(): MyDao
}

Below is how i insert data into the database:

@Inject
lateInt val database : MyDatabase

   override fun getAllItems(): Single<LiveData<MutableList<Item>>> {
     //retrieve new data using rertrofit
        networkController.getItems().map { responseItems ->
            saveAllItems(responseItems )
            getItems()
}

@Transaction
 fun saveAllItems(allItems: ItemsDataSource) {
    database.getProductDao().saveAllItems(allItems.loadedItems)
    database.getProductDao().saveAllItems(allItems.savedItems)
    database.getProductDao().saveAllItems(allItems.expiredItems)
    database.getProductDao().saveAllItems(allItems.unloadedItems)
}

fun getItems() : LiveData<MutableList<Item>>{

    return database.getProductDao().getAllItems()
}

My data source retrieved 4 lists of Items that i then save all of them in one entity/table but LiveData doesnt notify my UI about it?

ViewModel:

override fun getUnloadedOffers(): LiveData<MutableList<ProductOffer>> {
        if (!this::itemsLiveData.isInitialized) {
            itemsLiveData= MutableLiveData()
//get data from network or database
            itemDelegator.getItems()
                    .subscribeOn(Schedulers.io())
                    .observeOn(AndroidSchedulers.mainThread())
                    .subscribe({ items->
                        itemsLiveData= items

                    })
        }

        return itemsLiveData
    }

UI

viewModel = ViewModelProviders.of(this, viewModelFactory).get(MyViewModel::class.java)

     viewModel.getItems().observe(this, Observer {
                items->
                items?.let {
                    adapter = SomeAdapter(items)
                    itemsRecyclerView.adapter = adapter
                    adapter.notifyDataSetChanged()
                }

            })

Answer 1

Does your function getUnloadedOffers() return empty mutableList? I'm not sure if passing items to itemsLiveData is going to work, since observing LiveData is running on bg thread (if I'm not mistaken)

Answer 2

Try to use vararg instead of List when saving collection of data.

@Insert(onConflict = OnConflictStrategy.IGNORE)
fun saveAllItems(vararg itemList: Item)

And then you can call this method using * (also known as Spread Operator ) on your list like this

saveAllItems(*responseItems.toTypedArray())