20120903
========

- :mod:`lino.ui.extjs3.ext_store` : 
  added `DisabledFieldsStoreField.disabled_fields` 
  because GenericForeignKey has no attribute `editable`.
  
- :class:`Account <lino.modlib.accounts.models.Account>`:
  The new `ref` field now is blank=True but not null=True.
  If not specified, 
  a default value is being set in `full_clean`.

- :mod:`lino.modlib.outbox` : added new menu command 
  :menuselection:`Explorer --> Attachments`

- renamed lino.core.table to lino.core.dbtables,
  renamed lino.utils.tables to lino.core.tables

A subtile side effect occurs when lino_welfare tried 
to generate docs. 
Here is a snippet that reproduces it:

.. literalinclude:: 0903.py
 
It causes the following traceback::

  Traceback (most recent call last):
    File "0903.py", line 3, in <module>
      from lino_welfare.modlib.pcsw import models as pcsw
    File "t:\hgwork\welfare\lino_welfare\modlib\pcsw\models.py", line 1344, in <module>
      class UsersWithClients(dd.VirtualTable):
    File "t:\hgwork\lino\lino\core\actors.py", line 145, in __new__
      cls.add_virtual_field(k,v)
    File "t:\hgwork\lino\lino\core\actors.py", line 815, in add_virtual_field
      vf.lino_resolve_type(cls,name)
    File "t:\hgwork\lino\lino\core\fields.py", line 233, in lino_resolve_type
      self.return_type = resolve_field(self.return_type)
    File "t:\hgwork\lino\lino\core\modeltools.py", line 404, in resolve_field
      model = models.get_model(app_label,l[0])
    File "l:\snapshots\django\django\db\models\loading.py", line 213, in get_model
      self._populate()
    File "l:\snapshots\django\django\db\models\loading.py", line 67, in _populate
      self.load_app(app_name)
    File "l:\snapshots\django\django\db\models\loading.py", line 88, in load_app
      models = import_module('.models', app_name)
    File "l:\snapshots\django\django\utils\importlib.py", line 35, in import_module
      __import__(name)
    File "t:\hgwork\welfare\lino_welfare\modlib\jobs\models.py", line 88, in <module>
      from lino_welfare.modlib.pcsw import models as pcsw
  ImportError: cannot import name models  

The reason was that `lino_resolve_type` 
of virtual fields on actors was being called too early 
during the startup process. 
Here it triggered a premature call to _populate() Django's model cache.


Accessing virtual fields
------------------------

While working on the template for printing a sales invoice, 
I stumbled over a missing feature which I described as follows 
in the MTI tutorial (:mod:`lino.test_apps.mti`):

    :class:`lino.fields.VirtualField` instances are 
    no Django fields, Django ignores them and so doesn't 
    install the simple attribute instance get/set 
    access for them.
    That's why the following ``obj.is_restaurant`` does not 
    give ``False`` as you might expect.

      obj.is_restaurant
      <lino.utils.mti.EnableChild object at ...>

    This is not implemented because the only 
    need for it would be to make the following 
    examples more elegant...


Added the following simple `__get__` and `__set__` methods to 
:class:`lino.core.fields.VirtualField`::


    def __get__(self,instance,owner):
        if instance is None: return self
        return self.value_from_object(instance)

    def __set__(self,instance,value):
        return self.set_value_in_object(None,instance,value)

Which turns virtual fields into `descriptors
<http://docs.python.org/reference/datamodel.html#implementing-descriptors>`_.

So the above section from the MTI tutorial is no longer necessary 
because the feature is no longer missing.


Lino-Welfare
------------

- added `Account.ref` to debts std fixtures

- Researched on a mysterious message 
  "outbox.Attachment Controllers of Attachment must define a method `get_target_url`. (1 object(s) with primary key 1)"
  during data migration.