diff --git a/hr_avancys/models/hr_contract/hr_holiday_book.py b/hr_avancys/models/hr_contract/hr_holiday_book.py
index d1b36c9..5e843d0 100644
--- a/hr_avancys/models/hr_contract/hr_holiday_book.py
+++ b/hr_avancys/models/hr_contract/hr_holiday_book.py
@@ -79,7 +79,9 @@ class HrHolidayBook(models.Model):
     )
 
     def delete_lines(self, contract_id):
-        self._cr.execute("DELETE FROM hr_holiday_book WHERE contract_id = {id} and (manual = 'f' or manual is null)".format(id=contract_id.id))
+        holiday_book_ids = contract_id.holiday_book_ids
+        holiday_book_ids = holiday_book_ids.filtered(lambda hb: hb.manual is not True)
+        holiday_book_ids.unlink()
 
     def check_date_for_work(self, contract_id, date):
         days_work = list(set([int(x.dayofweek) for x in contract_id.resource_calendar_id.attendance_ids]))