How to fill non column field of entity in room library

Question

I have a class entity as below

@Entity
public class Task {    
    private String name; 
    private Integer ParentId;
    private Integer userId;   
    @Ignore         


        

Answer 1

I'm using Kotlin and I've had a similar problem, and below is how I solved it.

1. Add additional field with ?(question mark) for nullable, without @Ignore annotation

   @Entity(tableName = "task")
   data class Task (
       val name: String,
       val parentId: Integer,
       val userId: Integer,
       val noOfSubTask: Integer?
   )
   

2. Add additional field(noOfSubTask in this case) to every query that selects Task in DAO.

   @Dao
   interface TaskDao {
       @Query("SELECT *,(SELECT count(*) FROM Task b  WHERE a._id = b.ParentId ) AS noOfSubTask FROM Task a ")
       fun getTaskList(): LiveData>
   
       @Query("SELECT *, NULL AS noOfSubTask FROM Task WHERE name = :name")
       fun getTask(name: String): LiveData
   
       ...
   }
   

If this does not work, you can try RawQuery that was recently introduced in Google I/O 2018.