Update (or create) flow inside itself and emit this, Room, Flow, MVVM

Question

I have been creating an SMS app. I have a list of conversations stored in Room database as ConversationEntity.

This is my query:

@Query("SELECT * FROM conversation_entity ORDER BY timestamp DESC")
fun getAllConversations(): Flow<List<ConversationEntity>>

I would like to observe (collect) data from this query inside my repository class, but I have to map it to a List<Conversation>. I know how to collect this data, I known to map List<ConversationEntity> into List<Conversation>. But I have no idea how should I emit list of conversations?

I tried things like emit second flow from the first one, or use MutableStateFlow and set date by .value

Answer 1

I am still confused what you mean, since you said you know how to collect a Flow and how to map List to List. So anyway let me give it a try:

class DAO {
  @Query("SELECT * FROM conversation_entity ORDER BY timestamp DESC")
  fun getAllConversations(): Flow<List<ConversationEntity>>
}

class Repository(private val dao: Dao) {
  fun getConversations(): Flow<List<Converstaion>> {
    // this maps every emitted element of the flow
    return dao.getAllConversations.map { list: List<ConversationEntity> ->
      // and this maps every element in the list
      list.map { conversationEntity ->
        conversationEntity.mapToConversation()
      }
    }
  }
}

class ConversationMapper {
  // Maps ConversationEntity to Conversation
  fun ConversationEntity.mapToConversation(): Conversation {
    // I have no idea of the fields, so you have to implement this mapping function yourself.
    return Converation(...)
  }
}

And that's it. Here is how you can use it in your ViewModel:

class YourViewModel : ViewModel(private val repository: Repository) {
  val converstationLiveData: LiveData = repository.getConversations().toLiveData()
}

Hope that helps you. But if this is still not what you meant, then please update your question accordingly.