Hi Donald,

You would need to create a custom module for that, override the "_prepare_invoice_line" method and pass the value of the Purchase Date field of Sales Order Line.

Add following code in your custom module:

class SaleOrderLine(models.Model)
    _inherit = 'sale.order.line'

    @api.multi
    def _prepare_invoice_line(self):
        inv_line_vals = super(SaleOrderLine, self)._prepare_invoice_line()
        inv_line_vals.update({'pur_date': self.pur_date})
        return inv_line_vals

Let me know if you need any guidance in custom module.

Sudhir Arya
ERP Harbor Consulting Services
Skype:	sudhir@erpharbor.com
Website:	http://www.erpharbor.com

Sudhir, I chose the trigger method.  Here's what I learned:  At first I put the trigger on the account_invoice_line table.  My initial logic was to use the sale_order_line_invoice_rel table to relate sale order line to invoice line.  I got the function and trigger coded successfully, but it did not copy the date.  I figured out why:  the row is not inserted into the sale_order_line_invoice_rel table until AFTER the account_invoice_line row is successfully inserted.  So I changed my function and trigger to operate on the sale_order_line_invoice_rel table.  Here's my code:

-- DROP FUNCTION public.set_invoice_line_date_of_service();

CREATE OR REPLACE FUNCTION public.set_invoice_line_date_of_service()
  RETURNS trigger AS
$BODY$
DECLARE
  xdateofservice date;
BEGIN
  xdateofservice := x_date_of_service from sale_order_line where id = NEW.order_line_id;
  update account_invoice_line
    SET x_date_of_service = xdateofservice WHERE id = NEW.invoice_line_id;
  RETURN NEW;
END;
$BODY$
LANGUAGE plpgsql;


CREATE TRIGGER set_invoice_line_date_of_service
  AFTER INSERT
  ON public.sale_order_line_invoice_rel
  FOR EACH ROW
  EXECUTE PROCEDURE set_invoice_line_date_of_service();

I suppose I didn't need the "RETURN NEW" statement.  Am i right?  In any event, our company is a service company and we wanted a field in the table to keep track of when the service was provided and we could put that info on the invoice line.  As you see my trigger does indeed do that.  I added the x_date_of_service field to sale_order_line and account_invoice_line models, and I added the field to sale.order.form and account.invoice.form.  When we verify with the vendor that the service is complete we enter the date.  Then when we invoice the customer at month end, each invoice line has the date when service was complete.

Next we want to do this same logic with vendors, since each service is provided by a sub-contractor.  It is a one-for-one relation between sales and purchases.  So each time we send a sub-contractor to a job we generate a purchase order.  At week end we generate the vendor bills, and each bill has line items for each job that vendor worked, and so we want to put the date of service on each line.  Odoo business model doesn't exactly fit our business model, so we are making it fit.