[newforms-admin] Admin searches should use distinct, if query involves joins

[Andy Dustman <farcepest@…>]

I have a model that is searchable based on fields that are several levels of indirection away, i.e.

class Course:

    # ...
    sections = ManyToManyField(Section)

    class Admin:

        search_fields = ('name', '^sections__instructors__surname',
                         '^sections__instructors__username',
                         '^sections__call_no')

i.e. Courses refers to Sections which refers to Instructors which has a couple fields to search on. Sections may belong to more than one course, and Instructors may belong to more than one section. In the current trunk, a search on surname in this scheme can return the same Course multiple times.

To fix this, I simply changed django.contrib.admin.views.main.ChangeList.get_query_set() to return a QuerySet().distinct() all the time. This doesn't seem to break anything and it fixes the duplicate results problem. However, it's possible it may have some performance impact so you might want to make it conditional on whether or not the search is across joined tables. However, it wasn't really obvious how to do this so I went for the quick-and-(clean|dirty) solution.

[Andy Dustman <farcepest@…>]

Make all admin searches distinct

[Adrian Holovaty]

Yeah, I'm concerned about the performance impact that you pointed out. It should only add a DISTINCT if needed -- it should NOT always put that in.

I'm removing the [patch] designation.

[Andy Dustman <farcepest@…>]

Use distinct() only when joined search fields are present

[anonymous]

Requested changes made: As long as at least one field contains __, the resulting QuerySet will be made distinct().

One minor concern: I am explicitly looking for '__' in the field names and I wonder if I should look for LOOKUP_SEPARATOR from django.db.models.query. However a section above this (local function construct_search()) uses an explicit '__' and LOOKUP_SEPARATOR is not currently refererenced from outside of the module where it is defined, so I'm assuming it's OK.

[Malcolm Tredinnick]

(In [5123]) newforms-admin: Fixed #2818 -- Filtered out duplicate results when searching in
the admin across related fields. Thanks, Andy Dustman.