EF6 Use Existing Db Column as Discriminator

Question

I am using Entity Framework 6 Code First for my project. Entities have Inheritance so I am following TPH(Table per Hierarchy). I read following Article and many others.

None of them explain a way in which I can use an existing DB Column mapped to a property in Base Entity as Discriminator.

Based on the sample below I get following Exception

One or more validation errors were detected during model generation:

TaskType: Name: Each property name in a type must be unique. Property name 'TaskType' is already defined.

I think EF's auto generated Discriminator and my Entities Mapping is Conflicting.

Is there a possible way to instruct EF to not auto generate column and use Entity mapped Column. If not, is there any explanation of this can not be avoided.

Peace.

I have Entities in following format

public enum TaskType
{
    Random = 0,
    Polished = 1,
    Dropping = 2
}

public interface ITask
{
    int Id { get; set; }
    string Name { get; set; }
    TaskType typeofTask { get; set; }
}

public abstract class BaseTask : ITask
{
    public BaseTask(string name, TaskType type)
    {
        this.Name = Name;
        this.typeofTask = type;
    }
    public int Id { get; set; }
    public string Name { get; set; }
    public TaskType typeofTask { get; set; }
}

public class RandomTask : BaseTask
{
    public RandomTask() : base("My Random", TaskType.Random)
    {
    }
    public int Owner { get; set; }
}

public class PolishedTask : BaseTask
{
    public PolishedTask() : base("My Polished", TaskType.Polished)
    {

    }
}

public class DBContextTest : DbContext
{
    public DBContextTest(string connection) : base(connection)
    {

    }
    public DbSet<BaseTask> Task { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<BaseTask>().Map<RandomTask>(m => m.Requires("TaskType").HasValue(1))
           .Map<PolishedTask>(m => m.Requires("TaskType").HasValue(1));

        modelBuilder.Entity<BaseTask>().Property(p => p.typeofTask).HasColumnName("TaskType");
    }

}
class Program
{
    static void Main(string[] args)
    {
        try
        {
            DBContextTest dataContext = new DBContextTest("Server = (localdb)\\mssqllocaldb;DataBase = LOC2;Trusted_Connection = True;");
            RandomTask randomtask = new RandomTask();
            PolishedTask polishedTask = new PolishedTask();
            dataContext.Task.Add(randomtask);
            dataContext.Task.Add(polishedTask);
            dataContext.SaveChanges();
        }
        catch (System.Exception ex)
        {

        }

    }
}

Answer 1

Remove TaskType from your entity and let EF manage that as part of the TPH mapping. To differentiate types if you're dealing with a base-class collection, use .OfType<PolishedTask>() rather than .Where(x => x.TaskType == TaskType.Polished) EF should take care of the rest. If you do want it on the entity, create a non-mapped property in your sub-classes. I.e.

public abstract class BaseTask
{
  [NotMapped]
  public abstract TaskType TaskType { get; }
}

public class PolishedTask
{
  [NotMapped]
  public override TaskType TaskType => TaskType.Polished

  // or
  //public override TaskType TaskType
  //{
  //  get { return TaskType.Polished; }
  //}
}