Primary Key Violation: Inheritance using EF Code First

Question

I have following EF code first code. I am getting the following exception:

'GiftCouponPayment' does not contain an identity column.

The tables are successfully created in database. However, how can I get rid of this exception? Also, what is the reason for this exception?

Note: I am okay with any table schema as longs as the domain model (described using code first) is retained (and the data can be queried).

After continuing this exception, there is a another exception as below:

An error occurred while saving entities that do not expose foreign key properties for their relationships. The EntityEntries property will return null because a single entity cannot be identified as the source of the exception. Handling of exceptions while saving can be made easier by exposing foreign key properties in your entity types. See the InnerException for details.

{"Violation of PRIMARY KEY constraint 'PK_dbo.PaymentComponent'. Cannot insert duplicate key in object 'dbo.PaymentComponent'.\r\nThe statement has been terminated."}

Reference:

1. Entity Framework: Split table into multiple tables

Note: The resulting database schema is as shown below.

Code:

public class MyInitializer : CreateDatabaseIfNotExists<NerdDinners>
{
    //Only one identity column can be created per table.
    protected override void Seed(NerdDinners context)
    {
        //context.Database.ExecuteSqlCommand("CREATE UNIQUE INDEX IX_Payment_PayedTime ON Payment (PayedTime)");
        context.Database.ExecuteSqlCommand("DBCC CHECKIDENT ('Payment', RESEED, 1)");
        context.Database.ExecuteSqlCommand("DBCC CHECKIDENT ('GiftCouponPayment', RESEED, 2)");
        context.Database.ExecuteSqlCommand("DBCC CHECKIDENT ('ClubCardPayment', RESEED, 3)");
    }
}

//System.Data.Entity.DbContext is from EntityFramework.dll
public class NerdDinners : System.Data.Entity.DbContext
{
    public NerdDinners(string connString): base(connString)
    { 
    }

    protected override void OnModelCreating(DbModelBuilder modelbuilder)
    {
        //Fluent API - Plural Removal
        modelbuilder.Conventions.Remove<PluralizingTableNameConvention>();

        //Fluent API - Table per Concrete Type (TPC)
        modelbuilder.Entity<GiftCouponPayment>()
            .Map(m =>
            {
                m.MapInheritedProperties();
                m.ToTable("GiftCouponPayment");
            });

        modelbuilder.Entity<ClubCardPayment>()
            .Map(m =>
            {
                m.MapInheritedProperties();
                m.ToTable("ClubCardPayment");
            });
    }

    public DbSet<GiftCouponPayment> GiftCouponPayments { get; set; }
    public DbSet<ClubCardPayment> ClubCardPayments { get; set; }
    public DbSet<Payment> Payments { get; set; }
}

public abstract class PaymentComponent
{
    public int PaymentComponentID { get; set; }
    public int MyValue { get; set; }
    public abstract int GetEffectiveValue();
}

public partial class GiftCouponPayment : PaymentComponent
{
    public override int GetEffectiveValue()
    {
        if (MyValue < 2000)
        {
            return 0;
        }
        return MyValue;
    }
}

public partial class ClubCardPayment : PaymentComponent
{
    public override int GetEffectiveValue()
    {
        return MyValue;
    }
}

public partial class Payment
{
    public int PaymentID { get; set; }
    public List<PaymentComponent> PaymentComponents { get; set; }
    public DateTime PayedTime { get; set; }
}

Client:

    static void Main(string[] args)
    {
        Database.SetInitializer<NerdDinners>(new MyInitializer());
        string connectionstring = "Data Source=.;Initial Catalog=NerdDinners;Integrated Security=True;Connect Timeout=30";

        using (var db = new NerdDinners(connectionstring))
        {
            GiftCouponPayment giftCouponPayment = new GiftCouponPayment();
            giftCouponPayment.MyValue=250;
            
            ClubCardPayment clubCardPayment = new ClubCardPayment();
            clubCardPayment.MyValue = 5000;
                    
            List<PaymentComponent> comps = new List<PaymentComponent>();
            comps.Add(giftCouponPayment);
            comps.Add(clubCardPayment);

            var payment = new Payment { PaymentComponents = comps, PayedTime=DateTime.Now };
            db.Payments.Add(payment);

            int recordsAffected = db.SaveChanges();
        }
    }

Answer 1

You are not specifying the ID field for your TPC / TPT mappings. Even with inheritance you need to do this when not running a TPH mappings. (To note, I'm also not sure on the MapInheritedProperties() call... This is generally used for TPH... not TPT)

 //Fluent API - Table per Concrete Type (TPC)
 modelbuilder.Entity<GiftCouponPayment>()
      .HasKey(x => x.PaymentComponentID)
      .Map(m =>
      {
          m.MapInheritedProperties();
          m.ToTable("GiftCouponPayment");
      })
      .Property(x => x.PaymentComponentID)
      .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);

This needs to be on each and every class mapping from the concrete type. If it were me I would go with TPH mapping where GiftCoupon as well as the other inheritance mapping so you end up with 1 table to represent the entire tree of objects using a discriminator column.

Regardless... The other thing you are missing in your base class is:

public byte[] Version { get; set; }

And the associated mapping for:

Property(x => x.Version).IsConcurrencyToken()

Which allows for optimistic concurrency.

Hopefully this helps a bit, let me know if you need further assistance or clarification.

Answer 2

I see that my initial advice about TPC wasn't correct because you are also using FK in the base class - do you see the PaymentComponent table? It should not be there in case of TPC inheritance. Try to use TPT inheritance (remove MapInheritedProperties from your mapping). This will end with the same correct database. Don't use reseed. The Id will be controlled just by identity column in PaymentComponent table (as it is at the moment).

Answer 3

On your PaymentComponent class decorate the ID with KeyAttribute

[Key]
public int PaymentComponentID { get; set; }