If ModelAdmin.queryset returns a filtered QS don't require a 2nd count call

[Alex Gaynor]

There is an optimization that tests QuerySet.query.where to see if we can reuse a count call, however we don't apply this optimization aggressively enough.

[patchhammer]

admin-count.2.diff fails to apply cleanly on to trunk

[Aymeric Augustin]

Change UI/UX from NULL to False.

[Wiktor]

I've updated patch so it applies correctly on current master.
Also, test in original patch assumes that there are 6 queries to db (including messages framework).

Currently, before applying patch there are 5 of them (including duplicated COUNT(*):

(Pdb) pprint(connection.queries)
[{'sql': 'QUERY = \'SELECT "django_session"."session_key", "django_session"."session_data", "django_session"."expire_date" FROM "django_session" WHERE ("django_session"."session_key" = %s  AND "django_session"."expire_date" > %s )\' - PARAMS = (\'2nj8364ycp90oge7xl5tf9mviz7grety\', \'2013-02-23 17:53:11.374277\')',
  'time': '0.000'},
 {'sql': 'QUERY = \'SELECT "auth_user"."id", "auth_user"."password", "auth_user"."last_login", "auth_user"."is_superuser", "auth_user"."username", "auth_user"."first_name", "auth_user"."last_name", "auth_user"."email", "auth_user"."is_staff", "auth_user"."is_active", "auth_user"."date_joined" FROM "auth_user" WHERE "auth_user"."id" = %s \' - PARAMS = (100,)',
  'time': '0.001'},
 {'sql': 'QUERY = \'SELECT COUNT(*) FROM "admin_views_emptymodel" WHERE "admin_views_emptymodel"."id" > %s \' - PARAMS = (1,)',
  'time': '0.000'},
 {'sql': 'QUERY = \'SELECT COUNT(*) FROM "admin_views_emptymodel" WHERE "admin_views_emptymodel"."id" > %s \' - PARAMS = (1,)',
  'time': '0.000'},
 {'sql': 'QUERY = \'SELECT "admin_views_emptymodel"."id" FROM "admin_views_emptymodel" WHERE "admin_views_emptymodel"."id" > %s  ORDER BY "admin_views_emptymodel"."id" DESC\' - PARAMS = (1,)',
  'time': '0.000'}]

After patch was applied, COUNT(*) is executed once:

(Pdb) pprint(connection.queries)
[{'sql': 'QUERY = \'SELECT "django_session"."session_key", "django_session"."session_data", "django_session"."expire_date" FROM "django_session" WHERE ("django_session"."session_key" = %s  AND "django_session"."expire_date" > %s )\' - PARAMS = (\'5y65r95ng27kccdmkrtoo1qom7q4vhln\', \'2013-02-23 17:54:51.024189\')',
  'time': '0.000'},
 {'sql': 'QUERY = \'SELECT "auth_user"."id", "auth_user"."password", "auth_user"."last_login", "auth_user"."is_superuser", "auth_user"."username", "auth_user"."first_name", "auth_user"."last_name", "auth_user"."email", "auth_user"."is_staff", "auth_user"."is_active", "auth_user"."date_joined" FROM "auth_user" WHERE "auth_user"."id" = %s \' - PARAMS = (100,)',
  'time': '0.001'},
 {'sql': 'QUERY = \'SELECT COUNT(*) FROM "admin_views_emptymodel" WHERE "admin_views_emptymodel"."id" > %s \' - PARAMS = (1,)',
  'time': '0.000'},
 {'sql': 'QUERY = \'SELECT "admin_views_emptymodel"."id" FROM "admin_views_emptymodel" WHERE "admin_views_emptymodel"."id" > %s  ORDER BY "admin_views_emptymodel"."id" DESC\' - PARAMS = (1,)',
  'time': '0.000'}]

[Wiktor]

New patch created.

Pull request here:

​https://github.com/django/django/pull/820

[Wiktor Kolodziej <wiktor@…>]

In f07a5f0a21857204465019b4e68f914d31cb396a:

Fixed #11295: If ModelAdmin.queryset returns a filtered QS don't require a 2nd count call

Original patch rewritten, added tests and get_filters_params method for ChangeList class.
Thanks Alex for the report.

[Honza Král <Honza.Kral@…>]

In d7e835f76d81d66a6d8964dba20506a1c6e559d8:

Merge pull request #820 from viciu/11295

Fixed #11295: If ModelAdmin.queryset returns a filtered QS don't require a 2nd count call