Supposedly Room makes all the job in corutines aut...

# compose

[Pablo]

Supposedly Room makes all the job in corutines automatically under the hood, but now, in an insert, I'm getting this error:
Cannot access database on the main thread since it may potentially lock the UI for a long period of time.
That meand I need to make the dao insert function suspend and call it from a coruitine. Then why documentation says that rooms do that job automatically? why the codelabs show you all the daos without suspend? should I put suspend in every dao function then? I'm confussed

[Stylianos Gakis]

This has nothing to do with compose.
You're also not showing at all what you're doing already for people to even begin to help you

[Pablo]

Here you can see the Dao I created for the codelab:

@Dao
interface FlightsDao {
    @Query("SELECT * FROM airport ORDER BY passengers DESC")
    fun getAllAirports(): Flow<List<Airport>>

    @Query("SELECT * FROM airport WHERE iata_code LIKE '%'||:text||'%' OR name LIKE '%'||:text||'%' ORDER BY passengers DESC")
    fun getAirportsByIatOrName(text: String): Flow<List<Airport>>

    @Query("SELECT * FROM airport WHERE id NOT LIKE :id ORDER BY passengers DESC")
    fun getAllDifferentAirports(id: Int): Flow<List<Airport>>

    @Query("SELECT * FROM favorite")
    fun getFavorites(): Flow<List<Favorite>>

    @Query("SELECT EXISTS(SELECT * FROM favorite WHERE departure_code = :departureCode AND destination_code = :destinationCode)")
    fun checkIfFavoriteExists(departureCode: String, destinationCode: String): Boolean

    @Insert
    fun insertFavorite(favorite: Favorite)
}

[Pablo]

I followed the samples proposed by google in the documentation, and they never put suspend on the samples

[Pablo]

After using it, I got that exception, which forces me to put suspend on the insertFavorite function and to launch it by a coroutine, so I can't understand why, because supposedly Room works asynchronously and uses coroutines under the hood.

[Pablo]

Now I'm confussed and I don't know if I need to make suspend every function of the dao, or if only is the insert, why the insert yes and the other not. The other worked perfectly bytheway and didn't give me errors without suspend. And I don't understand why.

[Pablichjenkov]

Always suspend, you are doing an io operation. And always return a Result<T> sealed class . In the cases of writing the db like insert, return Result<Unit>.

[Rafael Tonholo]

Room indeed handles coroutines and will use the IO dispatcher behind the scenes when dealing with coroutines, however, it also handles non-coroutines cases. That is why you need to "instruct" Room on how you want to retrieve your data.

If you plan to use Room with coroutines, you must use suspend functions or functions that return `Flow`s. If your functions return a Flow, you don't need to make them suspend.

Here is a good read about Room with Coroutines that explains the difference between a function without and with a suspend modifier.

And here is a good read about using Room with Flow

There are cases where using only suspend functions is the best option and cases where using `Flow`s would fit better.

I suggest taking the time to read the Kotlin coroutines documentation. It will give you a better understanding of when to use the suspend modifier and when it's unnecessary.