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 faced the same problem a few days ago and had a look at this thread. I am using Kotlin data classes for creating database entities. Given that Kotlin data classes do not play well with inheritance subclassing was not a viable option. My solution was to use the @Embedded keyword in a wrapping class, as follows:

data class TaskToDisplay(@Embedded
                         var task: Task,
                         var noOfSubTask: Int = 0)

This solution does not create an additional column in the database and most importantly matches all Task's fields with Room's response columns.

Answer 2

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<List<Task>>
   
       @Query("SELECT *, NULL AS noOfSubTask FROM Task WHERE name = :name")
       fun getTask(name: String): LiveData<Task>
   
       ...
   }
   

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

Answer 3

You should move the @Ignore field outside of the constructor, like this:

Sample data:

@Entity(primaryKeys = ["id"])
data class User(
    @SerializedName("id")
    val id: Int,

    @SerializedName("name")
    val name: String,

    @SerializedName("age")
    val age: Int
) {
   @Ignore
   val testme: String?
}

Refer github discussion for more details

Answer 4

Create a sub class of Task suppose

public class TaskDisplayModel extends Task{

@Ignore
private transient int noOfSubTask;

}

Then your query will be

@Query("SELECT *,(SELECT count(*) FROM Task b  WHERE a._id = b.ParentId ) AS noOfSubTask FROM Task a ")
LiveData<List<TaskDisplayModel >> getTaskList();