class Invoice:
    __metaclass__ = PoolMeta
    __name__ = 'account.invoice'

    groupe = fields.Many2One(
           'forest_group.group',
            string=u'Groupement',
            help=u'Groupement',
            states=_STATES,
            depends=_DEPENDS
        )
    forest = fields.Many2One(
            'forest.forest',
            string=u'Forest',
            help=u'Forest',
            states=_STATES,
            depends=_DEPENDS,
            domain=[('owner', '=', Eval('partyid'))],
            on_change_with=['groupe'],
        )

    def on_change_with_forest(self):
        if self.groupe is None:
            return None

    partyid = fields.Integer(
            string=u'idp',
            on_change_with=['groupe'],
            readonly=True,
        )

    def on_change_with_partyid(self):
        if self.groupe is not None:
            return self.groupe.party.id