#34605: Add distinct support for ListFilters
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Reporter: Karolis Ryselis | Owner: nobody
Type: Uncategorized | Status: new
Component: Uncategorized | Version: 4.2
Severity: Normal | 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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Current implementation of {{{ChangeList.get_filters()}}} returns
may_have_duplicates, which only accounts for field list filters, but not
custom list filters where no field is used. One possibility is to add
{{{.distinct()}}} in the {{{queryset()}}} method of the filter, but it
prevents the objects to be deleted using changelist because
{{{.delete()}}} cannot be called after {{{.distinct()}}}. Another approach
is to use the approach from {{{ChangeList.get_queryset()}}} - subquery +
{{{Exists()}}} in filter's queryset, however, this adds unnecessary
complexity on the query if multiple such filters are applied or other
filters/search may have duplicates - it would then nest the subqueries,
which is suboptimal.
I am not sure about the best solution for this - maybe add method
may_have_duplicates on filter spec classes, which defaults to current
{{{lookup_needs_distinct}}} call for field filters and raises
{{{NotImplementedError}}} for the others?
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Ticket URL: <https://code.djangoproject.com/ticket/34605>
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