Hi,

For that you will need to customize the default _run_buy function.

Try to rewrite _run_buy function like below.

from collections import defaultdict
from dateutil.relativedelta import relativedelta
from itertools import groupby
from odoo import api, fields, models, SUPERUSER_ID, _
from odoo.addons.stock.models.stock_rule import ProcurementException


class StockRule(models.Model):
    _inherit = 'stock.rule'

    @api.model
    def _run_buy(self, procurements):
        """ passing manually entered product description when route is
         make_to_order """
        procurements_by_po_domain = defaultdict(list)
        errors = []
        for procurement, rule in procurements:

            # Get the schedule date in order to find a valid seller
            procurement_date_planned = fields.Datetime.from_string(
                procurement.values['date_planned'])
            schedule_date = (procurement_date_planned - relativedelta(
                days=procurement.company_id.po_lead))

            supplier = False
            if procurement.values.get('supplierinfo_id'):
                supplier = procurement.values['supplierinfo_id']
            else:
                supplier = procurement.product_id.with_company(
                    procurement.company_id.id)._select_seller(
                    partner_id=procurement.values.get("supplierinfo_name"),
                    quantity=procurement.product_qty,
                    date=schedule_date.date(),
                    uom_id=procurement.product_uom)

            # Fall back on a supplier for which no price may be defined.
            # Not ideal, but better than blocking the user.
            supplier = supplier or procurement.product_id._prepare_sellers(
                False).filtered(
                lambda
                    s: not s.company_id or s.company_id == procurement.company_id
            )[:1]

            if not supplier:
                msg = _(
                    'There is no matching vendor price to generate the purchase'
                    'order for product %s (no vendor defined, minimum quantity'
                    'not reached, dates not valid, ...). Go on the product form'
                    'and complete the list of vendors.') % (
                          procurement.product_id.display_name)
                errors.append((procurement, msg))

            partner = supplier.name
            # we put `supplier_info` in values for extensibility purposes
            procurement.values['supplier'] = supplier
            procurement.values['propagate_cancel'] = rule.propagate_cancel

            domain = rule._make_po_get_domain(procurement.company_id,
                                              procurement.values, partner)
            procurements_by_po_domain[domain].append((procurement, rule))

        if errors:
            raise ProcurementException(errors)

        for domain, procurements_rules in procurements_by_po_domain.items():
            # Get the procurements for the current domain.
            # Get the rules for the current domain. Their only use is to create
            # the PO if it does not exist.
            procurements, rules = zip(*procurements_rules)

            # Get the set of procurement origin for the current domain.
            origins = set([p.origin for p in procurements])
            # Check if a PO exists for the current domain.
            po = self.env['purchase.order'].sudo().search(
                [dom for dom in domain], limit=1)
            company_id = procurements[0].company_id
            if not po:
                # We need a rule to generate the PO. However the rule generated
                # the same domain for PO and the _prepare_purchase_order method
                # should only uses the common rules's fields.
                vals = rules[0]._prepare_purchase_order(company_id, origins,
                                                        [p.values for p in
                                                         procurements])
                # The company_id is the same for all procurements since
                # _make_po_get_domain add the company in the domain.
                # We use SUPERUSER_ID since we don't want the current user to
                # be follower of the PO.
                # Indeed, the current user may be a user without access to
                # Purchase, or even be a portal user.
                po = self.env['purchase.order'].with_company(
                    company_id).with_user(SUPERUSER_ID).create(vals)
            else:
                # If a purchase order is found, adapt its `origin` field.
                if po.origin:
                    missing_origins = origins - set(po.origin.split(', '))
                    if missing_origins:
                        po.write({'origin': po.origin + ', ' + ', '.join(
                            missing_origins)})
                else:
                    po.write({'origin': ', '.join(origins)})

            procurements_to_merge = self._get_procurements_to_merge(
                procurements)
            procurements = self._merge_procurements(procurements_to_merge)

            po_lines_by_product = {}
            grouped_po_lines = groupby(po.order_line.filtered(lambda
                                                                  l: not l.display_type and l.product_uom == l.product_id.uom_po_id).sorted(
                lambda l: l.product_id.id), key=lambda l: l.product_id.id)
            for product, po_lines in grouped_po_lines:
                po_lines_by_product[product] = self.env[
                    'purchase.order.line'].concat(*list(po_lines))
            po_line_values = []
            for procurement in procurements:
                org_values = self.env['sale.order'].search(
                    [('name', '=', procurement.origin)])
                for org in org_values.order_line:
                    description = org.name
                    po_lines = po_lines_by_product.get(
                        procurement.product_id.id,
                        self.env[
                            'purchase.order.line'])
                    po_line = po_lines._find_candidate(*procurement)

                    if po_line:
                        # If the procurement can be merge in an existing line.
                        # Directly write the new values on it.
                        vals = self._update_purchase_order_line(
                            description,
                            procurement.product_id,
                            procurement.product_qty, procurement.product_uom,
                            company_id,
                            procurement.values, po_line)
                        po_line.write(vals)
                    else:
                        # If it does not exist a PO line for current procurement.
                        # Generate the create values for it and add it to a list
                        # in order to create it in batch.
                        partner = procurement.values['supplier'].name

                        test = self.env[
                            'purchase.order.line']._prepare_purchase_order_line_from_procurement(
                            procurement.product_id, procurement.product_qty,
                            procurement.product_uom, procurement.company_id,
                            procurement.values, po)
                        test.update({'name': procurement.values.get(
                            'move_dest_ids').sale_line_id.name})
                        po_line_values.append(test)                self.env['purchase.order.line'].sudo().create(po_line_values)

Regards

@Anu

Thank you but it's true in the case of changing the field manually. I must have the value of sales.order.line.name in the field of purchase.order.line.name when the PO is generated automaticly in MTO rule (Make to Order).

You can write as following : 

Odoo v12

class StockRule(modeles.Model) :
    _inherit = "stock.rule"


    @api.multi
    def _prepare_purchase_order_line(self, product_id, product_qty, product_uom, values, po, partner):
        res = super(StockRule, self)._prepare_purchase_order_line(product_id, product_qty, product_uom, values, po, supplier)
        res['name'] = "write as per your requirement"
        return res

Hi,  

When we create purchase order the product the description field contain the product name+internal reference+Description for Vendors .you can change this or you can change the description by overriding the on change function of product.