Your module must have method which will update existing module res.partner or res.user ....

Working on similar project at this moment. My module require it as well. Must add if not exist a new customer/supplier and create a new order.

Will follow your subject :)

This is an example given me by Gerthard (new API)

<pre>

  self.env['sale.order'].create({

     'field': variable,

     'field2': variable2

     ...

})

</pre> 

another example: (of course you have to adapt it to your requirements)

vals = {
    'name': self.name,
    'date_order': self.appointment_date,
    'partner_id': self.patient.partner_id.id,
    'user_id': self.doctor.partner_id.user_id.id,
    'order_line': [[0, 0, {
        'name': self.consultations.name,
        'price_unit': self.consultations.list_price,
        'product_id': self.consultations.id,
    }]],
}
if pricelist_id:
    vals['pricelist_id'] = pricelist_id.id
    vals['currency_id'] = pricelist_id.currency_id.id
self.sale_id = self.env['sale.order'].create(vals)