#25403: A quite common use of .extra()
-------------------------------------+-------------------------------------
Reporter: PaoloC68 | Owner: nobody
Type: New feature | Status: new
Component: Database layer | Version: master
(models, ORM) |
Severity: Normal | Resolution:
Keywords: QuerySet.extra | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by akaariai):
I am convinced having something like
{{{
Post.objects.select_related(
latest_comment=Select(
'comments', queryset=Comments.objects.order_by('-created_at')
)
)
}}}
in Django is a great idea.
If we got .filter() to accept expressions, then you could do exactly the
same raw SQL query with expressions as the blog mentions. That is,
`extra(where=['(blog_id, added) IN %s' % (values,)])` ==
`.filter(RawSQL('(blog_id, added) IN %s', (values,))`.
Note that the .extra() version used in the blog post uses string
formatting. While as used in the blog post the query is safe, you might be
vulnerable to SQL injection attacks if you use the same pattern with user
editable char fields for example.
--
Ticket URL: <https://code.djangoproject.com/ticket/25403#comment:4>
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