Attaching the DbEntityEntry to Context - asp.net

Question

i am trying to implement a log system to the entitiy framework context.
i want to get the deleted element primary key when its state is deleted.
this is my code:
if (item.State == EntityState.Added || item.State == EntityState.Deleted) {
log = new dt_islemLog();
log.eskiDeger = null;
log.islem = (item.State == EntityState.Added) ? Enums.GetDBValue(Enums.islemDurum.EKLENDI) : Enums.GetDBValue(Enums.islemDurum.SILINDI);
log.islemYapanKullanici_id = kullaniciID;
log.nesneAd = item.Entity.GetType().Name;
log.oturum_id = oturumID;
log.zaman = DateTime.Now;
base.SaveChanges();
var ID = GetPrimaryKeyValue(item);
log.nesneID = ID != null ? ID.ToString() : null;
this.dt_islemLog.Add(log);
}
And this is the method that i get the primary key
object GetPrimaryKeyValue(DbEntityEntry entry) {
try {
if (entry.State == EntityState.Detached)
((IObjectContextAdapter)this).ObjectContext.Attach((System.Data.Entity.Core.Objects.DataClasses.IEntityWithKey)entry.Entity);
var objectStateEntry = ((IObjectContextAdapter)this).ObjectContext.ObjectStateManager.GetObjectStateEntry(entry.Entity);
return objectStateEntry.EntityKey.EntityKeyValues[0].Value;
}
catch(Exception ex) {
return null;
}
}
But i can't attach the (entry.Entitiy) to context because the cast operation is invalid. How can i get the primary key ?

Answer 1

If someone needs i have found the solution. i have updated the primary key method to like this
object GetPrimaryKeyValue(DbEntityEntry entry)
{
try
{
if (entry.State == EntityState.Detached)
this.Set(entry.Entity.GetType()).Attach(entry.Entity);
var objectStateEntry = ((IObjectContextAdapter)this).ObjectContext.ObjectStateManager.GetObjectStateEntry(entry.Entity);
return objectStateEntry.EntityKey.EntityKeyValues[0].Value;
}
catch
{
return null;
}
}