Commit faf6a911 authored by Artur Frysiak's avatar Artur Frysiak Committed by Tim Graham
Browse files

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

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.
parent a7639722

django/db/models/query.py

+6 −0
Original line number Diff line number Diff line
@@ -1060,6 +1060,12 @@ class ValuesQuerySet(QuerySet): 
        # QuerySet.clone() will also set up the _fields attribute with the

        # names of the model fields to select.



    def only(self, *fields):

        raise NotImplementedError("ValuesQuerySet does not implement only()")



    def defer(self, *fields):

        raise NotImplementedError("ValuesQuerySet does not implement defer()")



    def iterator(self):

        # Purge any extra columns that haven't been explicitly asked for

        extra_names = list(self.query.extra_select)

docs/ref/models/querysets.txt

+12 −3
Original line number Diff line number Diff line
@@ -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()

docs/releases/1.7.txt

+6 −0
Original line number Diff line number Diff line
@@ -616,6 +616,12 @@ Models 
  :attr:`~django.db.models.ForeignKey.limit_choices_to` when defining a

  ``ForeignKey`` or ``ManyToManyField``.



* Calling :meth:`only() <django.db.models.query.QuerySet.only>` and

  :meth:`defer() <django.db.models.query.QuerySet.defer>` on the result of

  :meth:`QuerySet.values() <django.db.models.query.QuerySet.values>` now raises

  an error (before that, it would either result in a database error or

  incorrect data).



Signals

^^^^^^^

tests/queries/tests.py

+10 −0
Original line number Diff line number Diff line
@@ -1275,6 +1275,16 @@ class Queries3Tests(BaseQuerysetTest): 
            Item.objects.datetimes, 'name', 'month'

        )



    def test_ticket22023(self):

        # only() and defer() are not applicable for ValuesQuerySet

        with self.assertRaisesMessage(NotImplementedError,

                "ValuesQuerySet does not implement only()"):

            Valid.objects.values().only()



        with self.assertRaisesMessage(NotImplementedError,

                "ValuesQuerySet does not implement defer()"):

            Valid.objects.values().defer()





class Queries4Tests(BaseQuerysetTest):

    def setUp(self):