The corresponding CLR type for entity type 'Employee' is not instantiable

Question

My error:

The corresponding CLR type for entity type 'Employee' is not instantiable and there is no derived entity type in the model that corresponds to a concrete CLR type

I'm trying to use migration in EF Core. I'm using a Code-First approach.

I have one abstract class named Employee which has properties like Id, Name, UserId.

My requirement is to specify whether an Employee is Contract or Permanent.

My code is as follows:

public abstract class Employee
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string UserId { get; set; }
    [ForeignKey("UserId")]
    public virtual ApplicationUser User { get; set; }
}

My concrete class:

public class Contract : Employee
{
    // Left empty because I don't want to add any other columns
}

public class Permanent : Employee
{
    // Left empty because I don't want to add any other columns
}

and my DbContext:

public class CoreDbContext : IdentityDbContext<ApplicationUser>
{
    public CoreDbContext(DbContextOptions<CoreDbContext> options)
        : base(options)
    {
    }

    public DbSet<Employee> Employees { get; set; }

    protected override void OnModelCreating(ModelBuilder builder)
    {
        builder.Entity<Contract>();
        builder.Entity<Permanent>();
        base.OnModelCreating(builder);        
    }
}

Correct me where I am wrong.

Answer 1

You will need to define a mapping of class Employee to a table, like this:

builder.Entity<Employee>().ToTable("Employee");

This uses the Table Per Class Hierarchy/Single Table Hierarchy mapping model, which uses a column as the discriminator between the different types that are stored on the same table.

Answer 2

Remove "abstract" from class definition. I don't know why it is like that.