#3732: inconsistent values('col1', 'col2').distinct().count()
----------------------------------------------------+-----------------------
Reporter: David S. <[EMAIL PROTECTED]> | Owner: adrian
Status: new | Component: Database
wrapper
Version: SVN | Keywords:
Stage: Unreviewed | Has_patch: 1
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A ValueQuerySet with selected columns and using distinct returns a count
that is accurate only if _result_cache exists--because it can get its
len().
If _result_cache does not exists then the SQL to fetch to count is
inaccurate because it relies on the PK rather than the selected columns.
For instance:
{{{
#!python
>>> cs = Course.objects.filter(subject__code="ACC",
course_num=207).values('subject', 'course_num')
>>> cs
[{'course_num': '207', 'subject': 'ACC'}, {'course_num': '207', 'subject':
'ACC'}]
>>> cs.count()
2
>>> cs.distinct().count()
2L
>>> csdistinct = cs.distinct()
>>> csdistinct.count()
2L
>>> csdistinct
[{'course_num': '207', 'subject': 'ACC'}]
>>> csdistinct.count()
1
}}}
The attached patch has been tested and works on Postgres and Oracle and,
though the documentation explicitly says it should work, it seems to fail
with SQLite (at least testing in its shell.)
--
Ticket URL: <http://code.djangoproject.com/ticket/3732>
Django Code <http://code.djangoproject.com/>
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