如何从房间数据库 android Kotlin 获取回调

Question

I want to get just row count as Int value from room database, not from initialized LiveData such as livedata.value?.size

Dao class

 @Dao 
interface MyDao {
    @Query("SELECT COUNT(*) FROM User")
    fun getUserCount(): Int
 }

Repository class

class MyRepository(private val myDao: MyDao) {    
    fun getUserCount() = myDao.getUserCount()
}

ViewModel class

class MyViewModel(application: Application) : AndroidViewModel(application) {
    fun getUserCount() = myRepository.getUserCount()
}

This is what I want. But as you know we need to access room database at background thread, not at mainthread

so I changed the code like this

Dao class

 @Dao 
interface MyDao {
    @Query("SELECT COUNT(*) FROM User")
    suspend fun getUserCount(): Int
 }

Repository class

class MyRepository(private val myDao: MyDao) {    
    suspend fun getUserCount() = myDao.getUserCount()
}

ViewModel class

class MyViewModel(application: Application) : AndroidViewModel(application) {
    fun getUserCount() = viewModelScope.launch {
            myRepository.getUserCount()
    }
}

if row count is 1, How can I get "1" as callback?

Answer 1

Use COUNT

@Query("SELECT COUNT(column_name or primary key column name) from table_name ")
fun getCount(): Long

call getCount() from repository