old_contents: # -*- coding: utf-8 -*-
  ##############################################################################
  #
  #    Author Vincent Renaville. Copyright 2012 Camptocamp SA
  #
  #    This program is free software: you can redistribute it and/or modify
  #    it under the terms of the GNU Affero General Public License as
  #    published by the Free Software Foundation, either version 3 of the
  #    License, or (at your option) any later version.
  #
  #    This program is distributed in the hope that it will be useful,
  #    but WITHOUT ANY WARRANTY; without even the implied warranty of
  #    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  #    GNU Affero General Public License for more details.
  #
  #    You should have received a copy of the GNU Affero General Public License
  #    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  ##############################################################################
  
  from openerp import models, api
  
  
  class AccountBankStatement(models.Model):
      _inherit = "account.bank.statement"
  
      @api.multi
      def button_confirm_bank(self):
          res = super(AccountBankStatement, self).button_confirm_bank()
          for st in self:
              for st_line in st.line_ids:
                  st_line.journal_entry_id.state = 'draft'
          return res
  
new_contents: # -*- coding: utf-8 -*-
  ##############################################################################
  #
  #    Author Vincent Renaville. Copyright 2012 Camptocamp SA
  #
  #    This program is free software: you can redistribute it and/or modify
  #    it under the terms of the GNU Affero General Public License as
  #    published by the Free Software Foundation, either version 3 of the
  #    License, or (at your option) any later version.
  #
  #    This program is distributed in the hope that it will be useful,
  #    but WITHOUT ANY WARRANTY; without even the implied warranty of
  #    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  #    GNU Affero General Public License for more details.
  #
  #    You should have received a copy of the GNU Affero General Public License
  #    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  ##############################################################################
  
  from openerp import models, api
  
  
  class AccountBankStatement(models.Model):
      _inherit = "account.bank.statement"
  
      @api.multi
      def button_confirm_bank(self):
          res = super(AccountBankStatement, self).button_confirm_bank()
          entries = self.mapped('line_ids.journal_entry_id')
          entries.write({'state': 'draft'})
          return res
  
subject: Use mapped method