#26296: Trick with extra fields
--------------------------------------+--------------------
Reporter: vvkuznetsov | Owner: nobody
Type: Cleanup/optimization | Status: new
Component: Documentation | Version: master
Severity: Normal | Keywords: db
Triage Stage: Unreviewed | Has patch: 1
Easy pickings: 1 | UI/UX: 0
--------------------------------------+--------------------
In documentation there's comment in `values()` section about some behavior
of `extra`
https://docs.djangoproject.com/en/1.9/ref/models/querysets/#django.db.models.query.QuerySet.values
{{{
If you use a values() clause after an extra() call, any fields defined by
a select argument in the extra() must be explicitly included in the
values() call. Any extra() call made after a values() call will have its
extra selected fields ignored.
}}}
It's points that any extra fields after values() call will be ignored. But
I think that it's not correct and need more description.
For example it could be not obvious that next simple construction will
cause exception and such an not obvious one!
{{{
User.objects.values('username').extra(select={'test_field':
1}).values('test_field', 'username')
FieldError: Cannot resolve keyword 'test_field' into field. Choices are:
date_joined, email, first_name, groups, id, is_active, is_staff,
is_superuser, last_login, last_name, logentry, password, test_field,
user_permissions, username
}}}
I want to point out that `test_field` is listed in choices that's very
confusing. It happens because of all checks is runs against `extra_select`
but error is uses `extra` as part of available choices.
{{{
sorted(list(get_field_names_from_opts(opts)) + list(self.extra)
+ list(self.annotation_select))
}}}
I can help you with this small change.
--
Ticket URL: <https://code.djangoproject.com/ticket/26296>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
--
You received this message because you are subscribed to the Google Groups
"Django updates" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
To view this discussion on the web visit
https://groups.google.com/d/msgid/django-updates/054.bad55ea7a632f07347a46a1c6a99ad2f%40djangoproject.com.
For more options, visit https://groups.google.com/d/optout.
