#26634: Add the ability to do subselects for querying versioned data
--------------------------------+--------------------------------------
Reporter: dhobbs | Owner: nobody
Type: Uncategorized | Status: new
Component: Uncategorized | Version: 1.8
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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Changes (by charettes):
* needs_better_patch: => 0
* needs_tests: => 0
* needs_docs: => 0
Old description:
> I have versioned data of the form:
>
> id (autogenerate)
> ref (uuid)
> version (integer)
>
> Each 'save' inserts a new version with the same ref and (version+1)
> version number.
> I'd like an easy way to say 'give me the latest versions' (ie. distinct
> on refs, with max(version)).
>
> The SQL looks like this:
>
> select * from myapp_project where
> id in (SELECT id from myapp_project p WHERE p.version = (SELECT
> max(version) FROM myapp_project p1 WHERE p1.ref = p.ref))
>
> I had to use extra(where=[maxids]) to achieve this*.
>
> *Where maxids = "id in (SELECT id from myapp_project p WHERE p.version =
> (SELECT max(version) FROM myapp_project p1 WHERE p1.ref = p.ref))"
>
> Stackoverflow discussion here:
> http://stackoverflow.com/questions/37303010/what-is-the-django-way-of-
> doing-a-subselect
New description:
I have versioned data of the form:
id (autogenerate)
ref (uuid)
version (integer)
Each 'save' inserts a new version with the same ref and (version+1)
version number.
I'd like an easy way to say 'give me the latest versions' (ie. distinct on
refs, with max(version)).
The SQL looks like this:
{{{#!sql
select * from myapp_project where
id in (SELECT id from myapp_project p WHERE p.version = (SELECT
max(version) FROM myapp_project p1 WHERE p1.ref = p.ref))
}}}
I had to use `extra(where=[maxids])` to achieve this*.
*Where `maxids = "id in (SELECT id from myapp_project p WHERE p.version =
(SELECT max(version) FROM myapp_project p1 WHERE p1.ref = p.ref))"`
Stackoverflow discussion here:
http://stackoverflow.com/questions/37303010/what-is-the-django-way-of-
doing-a-subselect
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Ticket URL: <https://code.djangoproject.com/ticket/26634#comment:1>
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