实体框架的TPC映射导致错误

Question

I have these models:

public class Person
{
    public int PersonId { get; set; }

    public string Name { get; set; }

    public int Age { get; set; }
}

public class Student : Person
{
    public int Payment { get; set; }
}

public class Teacher : Person
{
    public int Wage { get; set; }
}

And in database, I have two tables called Teachers and Students . I want to use Entity Framework's TPC mapping. My context class is:

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Person>()
        .Property(i => i.PersonId)
        .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);

        modelBuilder.Entity<Teacher>().Map(m =>
        {
            m.MapInheritedProperties();
            m.ToTable("Teacher", "dbo");
        }); 

        modelBuilder.Entity<Student>().Map(m =>
        {
            m.MapInheritedProperties();
            m.ToTable("Student", "dbo");
        }); 
    }

But when I want to add a teacher, I get this error:

The changes to the database were committed successfully, but an error occurred while updating the object context. The ObjectContext might be in an inconsistent state. Inner exception message: AcceptChanges cannot continue because the object's key values conflict with another object in the ObjectStateManager. Make sure that the key values are unique before calling AcceptChanges.

What's wrong here?

Answer 1

See this link :

The reason we got this exception is because DbContext.SaveChanges() internally invokes SaveChanges method of its internal ObjectContext. ObjectContext's SaveChanges method on its turn by default calls AcceptAllChanges after it has performed the database modifications.

AcceptAllChanges method merely iterates over all entries in ObjectStateManager and invokes AcceptChanges on each of them. Since the entities are in Added state, AcceptChanges method replaces their temporary EntityKey with a regular EntityKey based on the primary key values (ie PersonId ) that come back from the database and that's where the problem occurs since both the entities have been assigned the same value for their primary key by the database (ie on both PersonId = 1) and the problem is that ObjectStateManager cannot track objects of the same type with the same EntityKey value hence it throws. If you take a closer look at the TPC's SQL schema above, you'll see why the database generated the same values for the primary keys: the PersonId column in both Student and Teacher table has been marked as identity.

Try this:

public srting PersonId { get; set; }

and change your config to:

   modelBuilder.Entity<Person>()
        .Property(i => i.PersonId)
        .HasDatabaseGeneratedOption(DatabaseGeneratedOption.None);

and change you class to abstract /