Hello, i need help. I added job_title_2 in sale.order and want to bring job_title_2 field to account.invoice also automated field based on job_title or partner_id record. How to resolve this ?

class SaleOrder(models.Model):
    _inherit = 'sale.order'
	​​
	​job_title = fields.Char('Job Title')
	​job_title_2 = fields.Char('Job Title 2')

class AccountInvoice(models.Model):
    _inherit = 'account.invoice'
	​
	​job_title_2 = fields.Char('Job Title 2')

I'm overriding function but seems still not working

@api.multi
def _prepare_invoice(self):
    res = super(SaleOrderLine, self)._prepare_invoice()
    res['job_title'] = self.job_title
    res['job_title_2'] = self.job_title_2
    return res

What's wrong with my code ? thanks