[OutputCache(Duration =3600, VaryByCustom = "User")] //Global.asax override GetVaryByCustomString
        public ActionResult Index(...)
        {           
            string codiceUtente = Utility.Codice();
             
            var model = _dbContext.Ordini.Where( i=> i.codice == codiceUtente && ...altri filtri nella pagina
          
...
}


public override string GetVaryByCustomString(HttpContext context, string arg)
        { 
            if (arg.Equals("User", StringComparison.InvariantCultureIgnoreCase))
            {
                 //var x = System.Web.HttpContext.Current.User.Identity.Name;
                 var user = context.User.Identity;
                return string.Format("{0}", user.Name);
            }
            return base.GetVaryByCustomString(context, arg);
        }

public static String CodiceUtente()
        {
            string codice = null;
            using (MyDbEntitiesUsersContext db = new MyDbEntitiesUsersContext(@"xxx"))
            {
                codice = (from u in db.Utenti
                           where u.UserName == System.Web.HttpContext.Current.User.Identity.Name
                            select u.Codice).
                                            FirstOrDefault().ToString();
            }
            return codice;
        }