public bool AddImportBill(import_bill ib)
 {
     try
     {
         using (QLBH_PHONE_ENTITY data = new QLBH_PHONE_ENTITY())
         {
             data.import_bill.Add(ib);
             data.SaveChanges();
             return true;
         }
     }
     catch (Exception e)
     {
         Debug.WriteLine(e);
         return false;
     }
 }
 public bool UpdateImportBill(import_bill ib)
 {
     try
     {
         using (QLBH_PHONE_ENTITY data = new QLBH_PHONE_ENTITY())
         {
             data.Entry(ib).State = EntityState.Modified;
             data.SaveChanges();
             return true;
         }
     }
     catch (Exception e)
     {
         Debug.WriteLine(e);
         return false;
     }
 }