:date: 2020-09-01

==========================
Tuesday, September 1, 2020
==========================

Fixed some issues with learning foreign keys
============================================

I worked on :ticket:`3653`.
Summary of changes:
:term:`Learning foreign keys <learning foreign key>` now also work in :ref:`react`.
The :attr:`lino_xl.lib.cal.Guest.partner` field is now a :term:`learning foreign key`.

This didn't require any change in :ref:`react` because react actually handled
LFKs better than extjs. I rather adapted Lino to accept the react way as well.

I reviewed the internal API for defining learning FKs.
Removed the :attr:`disable_create_choice` attribute of :class:`lino.core.model.Model`.
The :meth:`lino.core.model.Model.choice_text_to_dict` method is now the only thing
to implement. When it returns a dict, then the database object gets created.
When it returns `None`, the user will see a warning.  Default implementation
returns `None`.  The only implemented usage so far is in `contacts.Person`.

NB it is still necessary to explicitly create a chooser and a
:meth:`create_FOO_choice` method.  But now the :meth:`create_FOO_choice` method
is a one-liner.

An easy place for reproducing the problem:

- go amici1, runserver, sign in as robin, go to the detail of some appointment.
  Click on the "Person" field in the Presences panel to add a new person. Type
  "Foo Bar" (name of a person that doesn't yet exist). Type Enter.

- Expected behaviour: Lino should create a person `(first_name="Foo",
  last_name="Bar")`.

- Actual behaviour: the JS console says
  SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSON data

It is --correctly-- sending a POST to
http://127.0.0.1:8000/api/cal/GuestsByEvent

And the POST request says::

  an=grid_post&mk=209&mt=24&partner=foo+bar&rp=weak-key-24

That is, it doesn't send a `partnerHidden` field, as it would when we select an
existing person::

  an=grid_post&mk=209&mt=24&partner=Odette+Adam&partnerHidden=227&rp=weak-key-24

The extjs front end worked because there the combobox puts the value "foo bar"
in both fields of the AJAX request (partner and partnerHidden). Which is not
very elegant. I changed Lino to support an empty partner field and to look up the
partnerHidden field for comboboxes of a learning FK.

:meth:`storeField.form2obj` has three steps:

- :meth:`extract_form_data`
- :meth:`parse_form_value`
- :meth:`set_value_in_object`

The code to create the partner is no longer executed in :meth:`parse_form_value`
but in :meth:`extract_form_data`. The internal "value" returned by
:meth:`extract_form_data` is no longer the parsed primary key but the model
instance (which potentially has been created on the fly).

In `ParameterStore.parse_params` we do not use the learning FK feature.

I moved the functions :func:`choices_response`  and :func:`choices_for_field`
from :mod:`lino_react.react.views` to :mod:`lino.core.views` and to
:mod:`lino.core.fields` because this was duplicated code. 

Another bug
===========

I opened :ticket:`3773`:
When I call, in react, in a slave table, the delete_selected action, react
doesn't specify the mk and mt parameters.  Which sometimes works (when the
master instance is not needed), but e.g. for a `cal.Guest` it failed.
:meth:`cal.GuestsByEvent.disable_delete` now raises an explicit exception in
that case::

  raise Exception("You must specify a master instance")


Reviewing the LETS tutorial
===========================

I realized that :ref:`lino.tutorial.lets` is actually a great example of
developing your own Lino application from scratch. A moved it to the "Getting
started" section of the developer guide.

I moved the code and the specs for lets1 into a new repository
https://gitlab.com/lino-framework/lets