I use the following code to update an object from servlet in Google App Engine :

String Time_Stamp=Get_Date_Format(6),query="select from "+Contact_Info_Entry.class.getName()+" where Contact_Id == '"+Contact_Id+"' order by Contact_Id desc";

PersistenceManager pm=null;
try
{
  pm=PMF.get().getPersistenceManager();

  // note that this returns a list, there could be multiple, DataStore does not ensure uniqueness for non-primary key fields
  List<Contact_Info_Entry> results=(List<Contact_Info_Entry>)pm.newQuery(query).execute();
  Contact_Info_Entry A_Contact_Entry=results.get(0);
  A_Contact_Entry.Extra_10=Time_Stamp;
  pm.makePersistent(A_Contact_Entry);
 }
catch (Exception e) { Send_Email(Email_From,Email_To,"Check_License_Servlet Error [ "+Time_Stamp+" ]",new Text(e.toString()+"\n"+Get_Stack_Trace(e)),null); }
finally { pm.close(); }

The value "[ 2010-05-13 Thu 15:58:31 ]" was in A_Contact_Entry.Extra_10, but it seems "pm.makePersistent(A_Contact_Entry);" was not executed. The object was not updated and there was no error message, why ? How to fix it ?