Code-First Primary Key Violation - ef-code-first

Question

I'm new to code-first, but love it. I have an inheritance structure: the nodes are coupled by a connection class. However, I suspect due to the PK, FK relationship between the base and derived classes there is is primary key violation.
Violation of PRIMARY KEY constraint 'PK_dbo.Connections'. Cannot insert duplicate key in object 'dbo.Connections'
So, not being a database Mack-O-Grady, I'm wondering if this is doable?
public abstract class Node
{
public Guid Id { get; set; }
}
[Table("Node1")]
public class Node1 : Node { }
[Table("Node2")]
public class Node2 : Node { }
[Table("Node3")]
public class Node3 : Node { }
public class Connection
{
public Guid Id { get; set; }
public Node Parent { get; set; }
public int ParentPort { get; set; }
public Node Child { get; set; }
}
public class TestContext : DbContext
{
public TestContext() : base("TST")
{
var ensureDLLIsCopied = System.Data.Entity.SqlServer.SqlProviderServices.Instance;
}
public DbSet<Node> Nodes { get; set; }
public DbSet<Connection> Connections { get; set; }
}
class Program
{
static void Main(string[] args)
{
var nodes = new List<Node>();
using (var context = new TestContext())
{
var n1 = new Node1
{
Id = Guid.NewGuid(),
};
nodes.Add(n1);
context.Nodes.Add(n1);
var n2 = new Node2
{
Id = Guid.NewGuid(),
};
nodes.Add(n2);
context.Nodes.Add(n2);
var n3 = new Node2
{
Id = Guid.NewGuid(),
};
nodes.Add(n3);
context.Nodes.Add(n3);
var c1 = new Connection { Parent = n1, ParentPort = 0, Child = n2 };
context.Connections.Add(c1);
var c2 = new Connection { Parent = n2, ParentPort = 0, Child = n3 };
context.Connections.Add(c2);
context.SaveChanges(); // exception when saving????
Console.ReadLine();
}
}
}

Answer 1

The answer is because the Id property (primary key wasn't being set)
var c1 = new Connection { Id = Guid.NewGuid(), Parent = n1, ParentPort = 0, Child = n2 };
context.Connections.Add(c1);
var c2 = new Connection { Id = Guid.NewGuid(), Parent = n2, ParentPort = 0, Child = n3 };
context.Connections.Add(c2);