public bool Login(PersonInfo personInfo)
        {
            bool result = false;
            try
            {
                this.Execute(() =>
                {
                    this.DataContext.DeferredLoadingEnabled = false;
                    var temp = from pi in this.DataContext.PersonInfos
                               where pi.PersonName == personInfo.PersonName && pi.Password == personInfo.Password
                               select pi;
                    var person = temp.SingleOrDefault();

                   if (person == null)
                    {
                        return false;
                    }
                    else
                    { 
                        return true; 
                    }
                });
            }
            catch (Exception ex)
            {
                SetErrorInfo(ex.Message, ex);
            }
            return result;
        }