#25028: annotation with Q object duplicates results
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Reporter: karyon | Owner: nobody
Type: Bug | Status: closed
Component: Uncategorized | Version: 1.8
Severity: Normal | Resolution: duplicate
Keywords: | 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):
This is a bit different from #10060, as there is no aggregation going on
here. The problem is that a single user has multiple groups, and you'll
get a different annotation for each of the groups.
You'll likely get the correct result if you add
`filter(Q(groups__name='group1')|Q(groups__isnull=True))` *before* the
annotate() call. This will work as the user can have at most one group
named group1.
I think there would be room for adding a generic query operator for asking
"annotate True to users which have at least (or at most) N groups matching
condition X". Your case is "at least 1 group named 'group1'", with the
extra constraint that group's name is unique. In the more general cases
answering this question requires aggregation. Notably you could also solve
your problem by conditional aggregation where you count all groups that
are named 'group1', and then annotate True if result is greater or equal
to 1.
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Ticket URL: <https://code.djangoproject.com/ticket/25028#comment:2>
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