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Code Issues 32 Releases Wiki Activity

queryset-refactor: Allow specifying of specific relations to follow in

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select_related(). Refs #5020.


git-svn-id: http://code.djangoproject.com/svn/django/branches/queryset-refactor@6899 bcc190cf-cafb-0310-a4f2-bffc1f526a37
This commit is contained in:
Malcolm Tredinnick
2007-12-09 06:24:17 +00:00
parent 3dce17ddc4
commit 3064a211bf
4 changed files with 143 additions and 22 deletions
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39
docs/db-api.txt
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@@ -744,8 +744,8 @@ related ``Person`` *and* the related ``City``::
p = b.author # Hits the database.
c = p.hometown # Hits the database.
Note that ``select_related()`` does not follow foreign keys that have
``null=True``.
Note that, by default, ``select_related()`` does not follow foreign keys that
have ``null=True``.
Usually, using ``select_related()`` can vastly improve performance because your
app can avoid many database calls. However, in situations with deeply nested
@@ -762,6 +762,41 @@ follow::
The ``depth`` argument is new in the Django development version.
**New in Django development version:** Sometimes you only need to access
specific models that are related to your root model, not all of the related
models. In these cases, you can pass the related field names to
``select_related()`` and it will only follow those relations. You can even do
this for models that are more than one relation away by separating the field
names with double underscores, just as for filters. For example, if we have
thise model::
class Room(models.Model):
# ...
building = models.ForeignKey(...)
class Group(models.Model):
# ...
teacher = models.ForeignKey(...)
room = models.ForeignKey(Room)
subject = models.ForeignKey(...)
...and we only needed to work with the ``room`` and ``subject`` attributes, we
could write this::
g = Group.objects.select_related('room', 'subject')
This is also valid::
g = Group.objects.select_related('room__building', 'subject')
...and would also pull in the ``building`` relation.
You can only refer to ``ForeignKey`` relations in the list of fields passed to
``select_related``. You *can* refer to foreign keys that have ``null=True``
(unlike the default ``select_related()`` call). It's an error to use both a
list of fields and the ``depth`` parameter in the same ``select_related()``
call, since they are conflicting options.
``extra(select=None, where=None, params=None, tables=None, order_by=None)``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~