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Wednesday, September 16, 2015
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Ticket #525
===========

I received and analyzed ticket :ticket:`525` (FieldError: Cannot
resolve keyword 'company' into field)

That's because the `Courses` table of the `courses` module used by
Lino Welfare à la Chatelet (which had been originally written for Lino
Faggio) still had a parameter field `city`. This makes sense only when
rooms are managed by external partners and thus have an address.

Wrote new test case :ref:`welfare.specs.courses2` to verify the fix.

The solution was to move this extended behaviour from
:mod:`lino.modlib.courses` to :mod:`lino_faggio.lib.courses`.

Which is yet another change in the master repo while Hamza is working
on :ticket:`505`.

Ticket #526
===========

In :mod:`lino_faggio.lib.courses` this extended behaviou actually does
not yet work because it causes the following error message::

  Exception: Cannot reuse detail_layout of <class 'lino.modlib.courses.models.ActivitiesByTeacher'> for <class 'lino.modlib.courses.models.ActivitiesBySlot'>

How to explain this message... Imagine that you have two plugin
libraries ``stdlib`` and ``mylib`` and that you want to extend a
plugin ``foo`` which (among others) overrides the `detail_layout` of
the `Foos` table.

In module ``stdlib.foo.models``::

    class Foos(Table):
        detail_layout = """
        a b c
        d
        """
     
    class FoosByA(Foos):
       ...
    
    class FoosByB(Foos):
       ...
    
In module ``mylib.foo.models``::

    from stdlib.foo.models import *

    class Foos(Table):
        detail_layout = """
        a b
        d e
        """
    
    class FoosByC(Foos):
       ...

    
In your application (in ``rt.models.foo``) you will have *four*
usable tables:

- `Foos` is defined in ``mylib``, inheriting from ``stdlib``
- `FoosByA` and `FoosByB` are defined in ``stdlib`` (you don't
  override them in ``mylib``)
- `FoosByC` is defined only in ``mylib``.

Now what should be the `detail_layout` of `FoosByA` and `FoosByB`?
The natural answer is that they should also get the overridden layout
defined for `Foos`.  This is why we have :meth:`set_detail_layout
<lino.core.actors.Actor.set_detail_layout>`. We must write module
``mylib.foo.models`` as follows::

    from stdlib.foo.models import *
    
    class FoosByC(Foos):
       ...
   
    @dd.receiver(dd.post_analyze)
    def customize_courses(sender, **kw):
        rt.models.foo.Foos.set_detail_layout("""
        a b
        d e
        """)

But this trick now doesn't work in the case of
:mod:`lino_faggio.lib.courses`.

I suggest to change :meth:`set_detail_layout
lino.core.actors.Actor.set_detail_layout>` so that it also updates all
derived tables. Which seems a bit dangerous and is not worth the
effort right now (since the original ticket :ticket:`525` is fixed).
Triggered this as new :ticket:`526`.