c# - Not updating discriminator when property type changes -

i've got entity has property that's abstract type. creates one-to-one relationship uses table-per-hierarchy inheritance. seems it's working correctly.

i can create item , set base property concreteone; saves correctly. however, when try update base concretetwo, ef updates base record in database new user value, doesn't update discriminator type. data concretetwo gets persisted, discriminator still says concreteone.

the following simple example exposes problem

namespace consoleapplication1 {     class program     {         static void main(string[] args)         {             app_start.entityframeworkprofilerbootstrapper.prestart();              database.setinitializer(new dropcreatedatabasealways<datacontext>());              // create our item concreteone base             using (var context = new datacontext())             {                 var item = new item                     {                         base = new concreteone { name = "item", data = 3 }                     };                 context.items.add(item);                 context.savechanges();             }              // update base new concretetwo             using (var context = new datacontext())             {                 var item = context.items.firstordefault();                  var newbase = new concretetwo()                     {                         item = item,                           name = "item 3",                          user = new user { name = "foo" }                     };                  // if don't set null, ef tries create new record in db causes pk exception                 item.base.item = null;                   item.base = newbase;                  // ef doesn't save discriminator, save user reference                 context.savechanges();             }              // retrieve item -- ef thinks base still concreteone             using (var context = new datacontext())             {                 var item = context.items.firstordefault();                 console.writeline("{0}: {1}", item.name, item.base.name);             }              console.writeline("done.");             console.readline();         }     }      public class datacontext : dbcontext     {         public dbset<item> items { get; set; }     }      public class user     {         public int id { get; set; }         public string name { get; set; }     }      public class item     {         public int id { get; set; }         public string name { get; set; }         public virtual base base { get; set; }     }      public abstract class base     {         public int id { get; set; }         public string name { get; set; }          [required]         public virtual item item { get; set; }     }      public class concreteone : base     {         public int data { get; set; }     }      public class concretetwo : base     {         public virtual user user { get; set; }     } } 

when changes saved, ef generates following sql:

update [dbo].[bases] set    [name] = 'item 3' /* @0 */,        [user_id] = 1 /* @1 */  (([id] = 1 /* @2 */)         , [user_id] null) 

so it's correct, i'd expect see [discriminator] = 'concretetwo' in update statement. expectations unfounded or doing wrong?

as test, tried using table-per-type , the entry removed concreteone table , added concretetwo table expect. works, real application has @ least 7 sub-types , sql statement retrieve base property got nasty. i'd accomplish using tph, if possible.

update: i've verified problem exists in ef5 ef6.

this question based on expectation of update taking place, seemingly debatable expectation. best bet if tph hierarchy not functioning expected, , considering ef6 in beta, start discussion on codeplex forums.