Room “Not sure how to convert a Cursor to this method's return type”: which method?

Question

Error:Not sure how to convert a Cursor to this method\'s return type
Error:Execution failed for task \':app:compileDebugJavaWithJavac\'.
Compilation failed; see the          


        

Answer 1

in case someone actually needs MutableLiveData<List<T>> in their ViewModel when working with Room and using Kotlin and coroutines, this is how I've solved it

In the Dao I get MutableList with suspend
In the repository I change the context to Dispatchers.IO and extract the list with suspend
in the ViewModel I use postValue with the list in the init, syntax is below

ViewModel

    private val allItems = MutableLiveData<List<DocumentItem>>()
    init {
        viewModelScope.launch {
            allItems.postValue(repository.getAll())
        }
    }

Repository

    suspend fun getAll(): MutableList<DocumentItem> = withContext(Dispatchers.IO) {
        dao.getAll()
    }

Dao

    @Query("SELECT * FROM document_items ORDER BY id DESC")
    suspend fun getAll(): MutableList<DocumentItem>

Answer 2

Modify your Dao, use Flowable instead of observable and add the following dependency (room with rxjava support)

compile group: 'android.arch.persistence.room', name: 'rxjava2', version: '1.1.1'

Dao returns flowable:

@Query("SELECT * FROM TableX")
public abstract Flowable<List<EntityX>> getAllXs();

Answer 3

For anyone landing here, using a coroutine Flow as a return type, you will get this error if you accidentally make the function suspend. Since it is returning a flow, there is no need to suspend.

So instead of this:

@Query("SELECT * FROM myTable WHERE id = :id")
suspend fun findById(id: Long): Flow<MyDataType>

use this (without suspend modifier):

@Query("SELECT * FROM myTable WHERE id = :id")
fun findById(id: Long): Flow<MyDataType> 

Answer 4

I Spend the entire day on this issue. the solution was very simple. I was using something like this before

@Query("SELECT * FROM myTable")
fun getAll(): MutableLiveData<ArrayList<myData>>

Now when I changed ArrayList to List & MutableLiveData to LiveData it is working fine.

@Query("SELECT * FROM myTable")
fun getAll(): LiveData<List<myData>>

based on the answers & comments on this issue I think room support only List & LiveData because I tried with on MutableLiveData & only ArrayList too. none of the combinations worked.

Hope this will help someones few hours.

Answer 5

Add the below code inside defaultConfig in build.gradle

javaCompileOptions.annotationProcessorOptions.includeCompileClasspath = true

Answer 6

In my case i was this problem when i used LiveData<ArrayList<Example Class>> in Dao class for getting all things from Room and i fixed this when i change ArrayList with List.

Example(Kotlin):

@Dao
interface ExampleDao {
@Query("SELECT * from example_table")
fun getAllExample():LiveData<List<Example>>
}