EntityFramework TPT继承

Question

I have a simple TPT Inheritance, EF 6.1.1

public class Base {
    public int Id {get; set;}
}

public class Derived : Base {
     public int SomeProperty {get; set;}
}

Note that in my case Base is NOT an abstract class, because in my domain can exists an instance of Base without Derived . DbContext :

public class ApplicationDbContext : DbContext {

   protected override void OnModelCreating(DbModelBuilder modelBuilder) {
       base.OnModelCreating(modelBuilder);

        modelBuilder.Entity<Derived >().ToTable("Derived");
   }

   public DbSet<Base> BaseDbSet {get ; set; }
   public DbSet<Derived> DerivedDbSet {get ; set; }
}

Now,

1. I can Insert in BaseDbSet.
2. I can Delete from BaseDbSet.
3. Deleting from DerivedDbSet deletes only the Derived Entity.
4. Inserting in the DerivedDbSet insert also a new record in the Base Table, also if the Id is correct, creating a new Id.

I really don't understand point 4. How can I insert a record in the derived table without inserting a new one in the Base table? I think the problem was related to identity column. It seems that when inserting EF doesn't care the Id of the Derived class, because the Id property has HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity) , but I cannot specify different DatabaseGeneratedOption attribute in Base and Derived class.

Answer 1

It is the expected behaviour. A Derived entity can not exist without Base entity.

If you are inserting a Derived entity wich Id is not in Base table, EF insert a new tuple in Base and in Derived , writing Id in Base table and SomeProperty in Derived table. Any other behavior produce data corruption and inconsistency.

If what you are trying is create a Derived from a existing Base just follow this link and read a bit.