Fields selected via extra() are omitted in ValuesQuerySet when fields are specified

[Jannis Vajen]

Books.objects.values().extra(select={'price_per_page': 'price / page'}) works fine.

Books.objects.values('book_id').extra(select={'price_per_page': 'price / page'}) however, does not.

[Russell Keith-Magee]

Working as designed. You've explicitly specified the values you want to be returned; if you want the extra column to be returned, you need to include it in the values() clause.

[Jannis Vajen]

Correct me if I'm wrong but don't the docs say the opposite?

If you use a values() clause after an extra() clause, any fields defined by a select argument in the extra() must be explicitly included in the values() clause. However, if the extra() clause is used after the values(), the fields added by the select will be included automatically.

​http://docs.djangoproject.com/en/dev/ref/models/querysets/#values

[Russell Keith-Magee]

Hrm. This requires further investigation. I was fairly certain that values + extra was fairly extensively tested (see the extra_regress regression tests), so either the documentation is incorrect, or the tests are incomplete or incorrect.

[Russell Keith-Magee]

Ok - this looks like a failure of documentation. The current behavior has been tested ​since at least the 1.0 branch, so the documentation hasn't reflected reality for some time.

[Jannis Vajen]

Maybe I should be asking this on the django-developers list but what is the rationale behind ignoring the extra-fields after a values() clause?

As values() has a ​grouping function when used in aggregation, it would be quite handy if additional fields could be added with extra().

[Malcolm Tredinnick]

In [16697]:

Corrected explanation of values() and extra() interaction in querysets.

Fixes #15546, refs #13455. The original documentation patch
inadvertently muddied the waters in one aspect and this commit tidies
that up.