Error when use suspend function with room dao methods

[yifeidesu]

I'm trying to make all database query / delete functions in the Dao class as suspend functions. I enabled kotlin coroutine in gradle, and add suspend keywork for all dao functions. Then build, and get errors for wrong param type for the auto generated dao methods.

In Dao class:

@Query("select * from myevent")
suspend fun all(): List<MyEvent> // I added the suspend keyword

@Delete
suspend fun deleteEvent(event: MyEvent)
...

Then build and get this error:

e: C:\Users\projectpath\app\build\tmp\kapt3\stubs\debug\com\robyn\myapp\data\source\local\EventsDao.java:39: error: Deletion methods must either return void or return int (the number of deleted rows).
    public abstract java.lang.Object deleteEventById(@org.jetbrains.annotations.NotNull()
                                     ^
e: C:\Users\projectpath\app\build\tmp\kapt3\stubs\debug\com\robyn\myapp\data\source\local\EventsDao.java:41: error: Query method parameters should either be a type that can be converted into a database column or a List / Array that contains such type. You can consider adding a Type Adapter for this.
    kotlin.coroutines.experimental.Continuation<? super kotlin.Unit> p1);

Error links navigate to code from the auto generated dao class:

...
@org.jetbrains.annotations.Nullable()
@android.arch.persistence.room.Delete()
public abstract java.lang.Object deleteAllEvents(@org.jetbrains.annotations.NotNull() // error indicates at this line
java.util.List<com.robyn.myapp.data.MyEvent> events, @org.jetbrains.annotations.NotNull()
kotlin.coroutines.experimental.Continuation<? super kotlin.Unit> p1); // error indicates at this line
...

I tried delete the generated dao class and rebuild to renegerate it, still get these errors. How can I fix this?

[jcornaz]

Adding the suspend keywork change the JVM signature of the function by adding another parameter.

this kotlin signature: suspend fun all(): List<MyEvent>
will be compiled to this java signature: public void all(cont: Continuation<List<MyEvent>>)

[yifeidesu]

Does it mean that I can not use suspend for the dao methods, because it will change signature?

[yifeidesu]

I see. I will call it in coroutine functions instead. Many thanks!

[jcornaz]

Does it mean that I can not use suspend for the dao methods, because it will change signature?

As far as I now, yes. At least if you use a library to generate the dao classes. But you can still provider helper on it.

interface EventStore {

  @Query("select * from myevent")
  fun all(): List<MyEvent>
}

// run async and await the result
suspend fun EventStore.awaitAll(): List<MyEvent> = async { all() }.await()

// ensure to run in a given context
suspend fun EventStore.awaitAll(): List<MyEvent> = withContext(CommonPool) { all() }

This are just a examples, it depends on what you really want to achieve.

[jcornaz]

And of course depending on library you use (especially if it is a Kotlin library), You may ask them to support suspending functions. Or even, improve the library yourself.

What is the library you use, if I may ask ? Spring ?

If it's spring, it looks like they decided to support Kotlin (https://spring.io/blog/2017/01/04/introducing-kotlin-support-in-spring-framework-5-0), they may support this use case, in the future.

[yifeidesu]

@jcornaz I'm using Room Persistence library for Android. So now I'm using suspend not directly in the dao class but on its wrapper methods. Also I'll try use it on the extension methods to avoid use it directly with @Query, just as the example you provided. I think for improvement, the ide can give a red squiggly line when user try to use suspend together with Room's @Query annotation. Thank you for the examples!

[Ikayh19]

@jcornaz I'm using Room Persistence library for Android. So now I'm using suspend not directly in the dao class but on its wrapper methods. Also I'll try use it on the extension methods to avoid use it directly with @Query, just as the example you provided. I think for improvement, the ide can give a red squiggly line when user try to use suspend together with Room's @Query annotation. Thank you for the examples!

where you able to resolve this issue? I have the same problems and can't figure out a solution