@api.model
def _prepare_attendee_values(self, registration):
    ' Override to add sale related stuff '
    line_id = registration.get('sale_order_line_id')
    if line_id:
        registration.setdefault('partner_id', line_id.order_id.partner_id)
    att_data = super(EventRegistration, self)._prepare_attendee_values(registration)
    if line_id:
        att_data.update({'event_id': line_id.event_id.id, 'event_id': line_id.event_id.id, 'event_ticket_id': line_id.event_ticket_id.id, 'origin': line_id.order_id.name, 'sale_order_id': line_id.order_id.id, 'sale_order_line_id': line_id.id})
    return att_data
Override to add sale related stuff
@api.model
def _prepare_attendee_values(self, registration):
    '  '
    line_id = registration.get('sale_order_line_id')
    if line_id:
        registration.setdefault('partner_id', line_id.order_id.partner_id)
    att_data = super(EventRegistration, self)._prepare_attendee_values(registration)
    if line_id:
        att_data.update({'event_id': line_id.event_id.id, 'event_id': line_id.event_id.id, 'event_ticket_id': line_id.event_ticket_id.id, 'origin': line_id.order_id.name, 'sale_order_id': line_id.order_id.id, 'sale_order_line_id': line_id.id})
    return att_data