old_contents: # -*- coding: utf-8 -*-
  # Copyright 2016 KMEE - Luis Felipe Miléo <mileo@kmee.com.br>
  # License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl).
  
  from openerp import api, fields, models, _
  
  
  class ResourceCalendar(models.Model):
  
      _inherit = 'resource.calendar'
  
new_contents: # -*- coding: utf-8 -*-
  # Copyright 2016 KMEE - Luis Felipe Miléo <mileo@kmee.com.br>
  # License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl).
  
  from openerp import api, fields, models, _
  
  
  class ResourceCalendar(models.Model):
  
      _inherit = 'resource.calendar'
  
      parent_id = fields.Many2one(
          'resource.calendar',
          string='Parent Calendar',
          ondelete='restrict',
          index=True)
      child_ids = fields.One2many(
          'resource.calendar', 'parent_id',
          string='Child Calendar')
      _parent_store = True
      parent_left = fields.Integer(index=True)
      parent_right = fields.Integer(index=True)
  
      @api.constrains('parent_id')
      def _check_hierarchy(self):
          if not self._check_recursion():
              raise models.ValidationError(
                  'Error! You cannot create recursive calendars.')
  
subject: Add calendar hierarchy