#30079: Prefetch cache should be aware of database source and .using() should
not
always trigger a new query
-------------------------------------+-------------------------------------
Reporter: Mike Lissner | Owner: nobody
Type: | Status: closed
Cleanup/optimization |
Component: Documentation | Version: master
Severity: Normal | Resolution: wontfix
Keywords: prefetch, | Triage Stage:
multidatabase | Unreviewed
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Changes (by Carlton Gibson):
* status: new => closed
* resolution: => wontfix
* has_patch: 0 => 1
* component: Database layer (models, ORM) => Documentation
Comment:
OK, at best, this is a cleanup on the documentation. The admonition note
in the
[https://docs.djangoproject.com/en/2.1/ref/models/querysets/#django.db.models.query.QuerySet.prefetch_related
`prefech_related` docs] already covers this:
> Remember that, as always with **QuerySets**, any subsequent chained
methods which imply a different database query will ignore previously
cached results, and retrieve data using a fresh database query.
`using()` is a ''subsequent chained method''. It returns a new QuerySet,
and the results and prefetch caches are not transferred.
Arguably, `using()`, whilst returning a new QuerySet, doesn't actually
imply a different query.
As such I drafted the attached patch.
> ... as always with ``QuerySets``, any subsequent chained methods which
return a new ``QuerySet``, normally implying a different database query
...
In my opinion, the patch unnecessarily complicates the meaning. We know
from our use of QuerySets that all the
[https://docs.djangoproject.com/en/2.1/ref/models/querysets/#methods-that-
return-new-querysets Methods that return new QuerySets] behave this way,
even if we might forget it occasionally. Thus `wontfix`.
Thanks for the report Mike!
--
Ticket URL: <https://code.djangoproject.com/ticket/30079#comment:3>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
--
You received this message because you are subscribed to the Google Groups
"Django updates" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
To view this discussion on the web visit
https://groups.google.com/d/msgid/django-updates/066.9a293191d2f6aaf304c853bc39b82b11%40djangoproject.com.
For more options, visit https://groups.google.com/d/optout.
