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Fixed #22023 -- Raised an error for values() followed by defer() or only().

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Previously, doing so resulted in invalid data or crash.

Thanks jtiai for the report and Karol Jochelson,
Jakub Nowak, Loic Bistuer, and Baptiste Mispelon for reviews.
This commit is contained in:
Artur Frysiak 2014-02-15 22:44:14 +01:00 • committed by Tim Graham
parent a7639722f5
commit faf6a911ad
4 changed files with 34 additions and 3 deletions
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15
docs/ref/models/querysets.txt
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@ -502,14 +502,23 @@ A few subtleties that are worth mentioning:
made after a ``values()`` call will have its extra selected fields
ignored.
* Calling :meth:`only()` and :meth:`defer()` after ``values()`` doesn't make
sense, so doing so will raise a ``NotImplementedError``.
.. versionadded:: 1.7
The last point above is new. Previously, calling :meth:`only()` and
:meth:`defer()` after ``values()`` was allowed, but it either crashed or
returned incorrect results.
A ``ValuesQuerySet`` is useful when you know you're only going to need values
from a small number of the available fields and you won't need the
functionality of a model instance object. It's more efficient to select only
the fields you need to use.
Finally, note a ``ValuesQuerySet`` is a subclass of ``QuerySet``, so it has all
methods of ``QuerySet``. You can call ``filter()`` on it, or ``order_by()``, or
whatever. Yes, that means these two calls are identical::
Finally, note that a ``ValuesQuerySet`` is a subclass of ``QuerySet`` and it
implements most of the same methods. You can call ``filter()`` on it,
``order_by()``, etc. That means that these two calls are identical::
Blog.objects.values().order_by('id')
Blog.objects.order_by('id').values()