purchase_order_back2draft/models/purchase_order.py

# -*- encoding: utf-8 -*-

from openerp import models, api, exceptions, _


class PurchaseOrder(models.Model):
    _inherit = "purchase.order"

    @api.multi
    def button_purchase_draft(self):
        # go from canceled state to draft state
        for order in self:
            order.order_line.write({'state': 'draft'})
            for line in order.order_line:
                line.procurement_ids.sudo().unlink()
            order.write({'state': 'draft'})
            order.delete_workflow()
            order.create_workflow()
        return True