:date: 2021-03-19

======================
Friday, March 19, 2021
======================

I started the :mod:`lino_xl.lib.webshop` plugin, with Sharif watching me. It
(currently) has four database models Cart, CartItem, Address and PaymentMethod.
It needs and uses the existing plugins vat, sales, contacts, products,
ledger,... I also added a demo project of same name "webshop".

We discovered and fixed :ticket:`4036`.
We had (simplified) the following construct::

  class UserPlan(dd.Model):
      class Meta:
          abstract = True

      start_plan = StartPlan()

  class StartPlan(dd.Action):
    ...
    def run_from_ui(self, ar, **kw):
        options = self.get_options(ar)
        pm = self.get_plan_model(ar)
        ...

    def get_plan_model(self, ar):
        return self.defining_actor.model

Explanation: When the application has more than one concrete model that inherits
from :class:`lino.modlib.users.UserPlan`,  Lino's behaviour was wrong. Calling
:class:`webshop.Cart.start_plan <lino.modlib.users.UserPlan.start_plan>` created
an instance of :class:`lino_xl.lib.sheets.Report`, the concrete model that
happens to be the first to use it.

I fixed this by saying::

  class StartPlan(dd.Action):

    def get_plan_model(self, ar):
        return ar.actor.model


I stumbled into a similar pitfall: The quick link 'webshop.MyCart.start_plan'
was getting bound to the start_plan action on `lino_xl.lib.sheets.Report`. This
was caused by the :func:`lino.core.actors.resolve_action`. I optimized the
behaviour of this function and added test coverage in :ref:`dev.xlmenu`.

How to link user and partner? A normal webshop user fills in their postal
address or other contact data. Webshop adds the possibility to define multiple
invoicing and delivery addresses.
The partners of the users are not our partners. The partner of the generated invoices is always a same partner, stored in
the User.partner field and leading to a given sales.SalesRule.

The ar.success "x items have been placed to your shopping cart!" didn't not
show up because I must say `alert=True`.

The :class:`lino_xl.lib.webshop.AddToCart` action made us stumble into another
pitfall: when an action uses :meth:`ar.confirm
<lino.core.requests.BaseRequest.confirm>`, then the implementing code is being
called several times, once for each call to :meth:`ar.confirm
<lino.core.requests.BaseRequest.confirm>`. And each time the full text of the
confirmation message must remain the same.