Resource resource = dao.GetById(1);
dao.Evict(resource);
resource.Id = -1;   // my unsaved value is -1
Resource savedResource = dao.Save(resource);
dao.CommitChanges();
Console.WriteLine(savedResource.Id);    // outputs 45

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
  <class name="HELM.Domains.Payments,HELM.Domains" table="Payment" lazy="false" >
    <id name="Paymentid" column="PaymentID" type="System.Int32">
      <generator class="increment"/>
    </id>
      <property column="LastName" type="System.String" name="LastName" />
      <property column="FirstName" type="System.String" name="FirstName" />
      <property column="Address1" type="System.String" name="Address1" />
      <property column="Address2" type="System.String" name="Address2" />
      <property column="City" type="System.String" name="City" />
      <property column="State" type="System.String" name="State" />
      <property column="Zip" type="System.String" name="Zip" />
      <property column="Phone" type="System.String" name="Phone" />
  </class>
</hibernate-mapping>

//payment retries loop for PK violation
            for (int i = 0; i < 10; i++)
            {
                try
                {

                    //we need a paymentID and an OrderID before we can send
                    //the payment to the CGW
                    PersistenceManager.Save(payment, false);

                    theReturn = ProcessPayment(payment);

                    //process the payment
                    if (theReturn.Result == false)
                    {
                        //payment declined
                        PaymentDeclined(payment);
                    }
                    else
                    {
                        PaymentAuthorized(payment);
                    }

                    //save the payment
                    PersistenceManager.SaveOrUpdate(payment, true);

                    //no pk errors, leave our loop
                    break;
                }
                catch (Exception ex)
                {

                    Exception innerMostException = ex;

                    //get the inner-most exception
                    while (innerMostException.InnerException != null)
                    {
                        innerMostException = innerMostException.InnerException;
                    }

                    if (innerMostException.GetType() == typeof(SqlException))
                    {
                        //these error numbers are all error numbers for PK violations
                        if (((SqlException)innerMostException).Number != 547 && ((SqlException)innerMostException).Number != 2627 && ((SqlException)innerMostException).Number != 2607)
                        {
                            //something other than a PK violation and this loop
                            //isn't here to handle that
                            throw new Exception("Unable to apply payment. \n\n\n" + "message is: \n\n" + ex.Message);
                        }
                        else
                        {
                            payment.Paymentid = 0;
                        }
                    }
                    else
                    {
                        //something other than a PK violation and this loop
                        //isn't here to handle that
                        throw new Exception("Unable to apply payment. \n\n\n" + "message is: \n\n" + ex.Message);
                    }
                }
            }