:date: 2019-11-26

==========================
Tuesday, November 26, 2019
==========================

On the :class:`tickets.Ticket` class we now have the following::

    comments = GenericRelation('comments.Comment',
        content_type_field='owner_type', object_id_field='owner_id',
        related_query_name="ticket")

I thought it is a pity that we had no ticket with more than one comment in our
demo data.  So I changed that in the :fixture:`demo2` fixture of
:mod:`lino.modlib.comments`.

>>> from lino import startup
>>> startup('lino_book.projects.team.settings.demo')
>>> from lino.api.doctest import *

On every ticket we now have an attribute :attr:`comments` which is an object
manager that returns all the comments pointing to this ticket, i.e. that have
:attr:`lino.modlib.comments.Comment.owner` set to this ticket.  Similar to the
related_name of a ForeignKey, but for a GenericForeignKey.

>>> obj = tickets.Ticket.objects.get(pk=1)
>>> list(obj.comments.all())
[Comment #85 ('Comment #85'), Comment #86 ('Comment #86'), Comment #87 ('Comment #87'), Comment #88 ('Comment #88'), Comment #89 ('Comment #89'), Comment #90 ('Comment #90'), Comment #91 ('Comment #91'), Comment #92 ('Comment #92')]

And because we specified the `related_query_name` ``"ticket"``, we *also* have a
virtual field named :attr:`ticket` on each comment which contains almost the
same as the GFK :attr:`owner`, but only if that owner is a ticket.

>>> obj = comments.Comment.objects.get(pk=85)
>>> obj.owner #doctest: +ELLIPSIS
Ticket #1 ('#1 (⚹ Föö fails to bar when baz)')

>>> obj.ticket.first()
Ticket #1 ('#1 (⚹ Föö fails to bar when baz)')

The `ticket` field is implemented as an object manager, that's why we must call
:meth:`first` to get the actual ticket.  Don't ask me why.

>>> obj.ticket #doctest: +ELLIPSIS
<django.db.models.fields.related_descriptors.create_reverse_many_to_one_manager.<locals>.RelatedManager object at ...>

We can ask them all, but there will always be either one or no ticket.

>>> list(obj.ticket.all())
[Ticket #1 ('#1 (⚹ Föö fails to bar when baz)')]

That worked fine already yesterday.  The problem I stumbled into today was that
Lino did not yet support remote fields on the reverse generic relation. For
example to show, in a table of comments, the site of the ticket of a comment.

>>> rt.login("robin").show(comments.Comments,
... column_names="id owner owner_type ticket__site", offset=82, limit=6)
... #doctest: +ELLIPSIS +NORMALIZE_WHITESPACE +REPORT_UDIFF
==== =============================================== ====================== ========
 ID   Controlled by                                   Controlled by (type)   Site
---- ----------------------------------------------- ---------------------- --------
 83   `Developers <Detail>`__                         Team
 84   `Managers <Detail>`__                           Team
 85   `#1 (⚹ Föö fails to bar when baz) <Detail>`__   Ticket                 welket
 86   `#1 (⚹ Föö fails to bar when baz) <Detail>`__   Ticket                 welket
 87   `#1 (⚹ Föö fails to bar when baz) <Detail>`__   Ticket                 welket
 88   `#1 (⚹ Föö fails to bar when baz) <Detail>`__   Ticket                 welket
==== =============================================== ====================== ========
<BLANKLINE>


>>> from django.db.models import Q
>>> flt1 = Q(private=True)
>>> flt2 = Q(private=False)
>>> comments.Comment.objects.filter(flt1|flt2).count()