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Fixed #20988 -- Added model meta option select_on_save 

The option can be used to force pre 1.6 style SELECT on save behaviour.
This is needed in case the database returns zero updated rows even if
there is a matching row in the DB. One such case is PostgreSQL update
trigger that returns NULL.

Reviewed by Tim Graham.

Refs #16649
This commit is contained in:
Anssi Kääriäinen 2013-08-30 09:41:07 +03:00
parent 13be3bfef1
commit e973ee6a98
7 changed files with 130 additions and 16 deletions
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18
django/db/models/base.py
View File

@ -667,7 +667,9 @@ class Model(six.with_metaclass(ModelBase)):
base_qs = cls._base_manager.using(using)
values = [(f, None, (getattr(self, f.attname) if raw else f.pre_save(self, False)))
for f in non_pks]
updated = self._do_update(base_qs, using, pk_val, values, update_fields)
forced_update = update_fields or force_update
updated = self._do_update(base_qs, using, pk_val, values, update_fields,
forced_update)
if force_update and not updated:
raise DatabaseError("Forced update did not affect any rows.")
if update_fields and not updated:
@ -691,21 +693,27 @@ class Model(six.with_metaclass(ModelBase)):
setattr(self, meta.pk.attname, result)
return updated
def _do_update(self, base_qs, using, pk_val, values, update_fields):
def _do_update(self, base_qs, using, pk_val, values, update_fields, forced_update):
"""
This method will try to update the model. If the model was updated (in
the sense that an update query was done and a matching row was found
from the DB) the method will return True.
"""
filtered = base_qs.filter(pk=pk_val)
if not values:
# We can end up here when saving a model in inheritance chain where
# update_fields doesn't target any field in current model. In that
# case we just say the update succeeded. Another case ending up here
# is a model with just PK - in that case check that the PK still
# exists.
return update_fields is not None or base_qs.filter(pk=pk_val).exists()
else:
return base_qs.filter(pk=pk_val)._update(values) > 0
return update_fields is not None or filtered.exists()
if self._meta.select_on_save and not forced_update:
if filtered.exists():
filtered._update(values)
return True
else:
return False
return filtered._update(values) > 0
def _do_insert(self, manager, using, fields, update_pk, raw):
"""

4
django/db/models/options.py
View File

@ -22,7 +22,8 @@ DEFAULT_NAMES = ('verbose_name', 'verbose_name_plural', 'db_table', 'ordering',
'unique_together', 'permissions', 'get_latest_by',
'order_with_respect_to', 'app_label', 'db_tablespace',
'abstract', 'managed', 'proxy', 'swappable', 'auto_created',
'index_together', 'app_cache', 'default_permissions')
'index_together', 'app_cache', 'default_permissions',
'select_on_save')
@python_2_unicode_compatible
class Options(object):
@ -35,6 +36,7 @@ class Options(object):
self.ordering = []
self.unique_together = []
self.index_together = []
self.select_on_save = False
self.default_permissions = ('add', 'change', 'delete')
self.permissions = []
self.object_name, self.app_label = None, app_label

17
docs/ref/models/instances.txt
View File

@ -305,16 +305,23 @@ follows this algorithm:
* If the object's primary key attribute is *not* set or if the ``UPDATE``
didn't update anything, Django executes an ``INSERT``.
.. versionchanged:: 1.6
Previously Django used ``SELECT`` - if not found ``INSERT`` else ``UPDATE``
algorithm. The old algorithm resulted in one more query in ``UPDATE`` case.
The one gotcha here is that you should be careful not to specify a primary-key
value explicitly when saving new objects, if you cannot guarantee the
primary-key value is unused. For more on this nuance, see `Explicitly specifying
auto-primary-key values`_ above and `Forcing an INSERT or UPDATE`_ below.
.. versionchanged:: 1.6
Previously Django did a ``SELECT`` when the primary key attribute was set.
If the ``SELECT`` found a row, then Django did an ``UPDATE``, otherwise it
did an ``INSERT``. The old algorithm results in one more query in the
``UPDATE`` case. There are some rare cases where the database doesn't
report that a row was updated even if the database contains a row for the
object's primary key value. An example is the PostgreSQL ``ON UPDATE``
trigger which returns ``NULL``. In such cases it is possible to revert to the
old algorithm by setting the :attr:`~django.db.models.Options.select_on_save`
option to ``True``.
.. _ref-models-force-insert:
Forcing an INSERT or UPDATE

22
docs/ref/models/options.txt
View File

@ -256,6 +256,28 @@ Django quotes column and table names behind the scenes.
If ``proxy = True``, a model which subclasses another model will be treated as
a :ref:`proxy model <proxy-models>`.
``select_on_save``
------------------
.. attribute:: Options.select_on_save
.. versionadded:: 1.6
Determines if Django will use the pre-1.6
:meth:`django.db.models.Model.save()` algorithm. The old algorithm
uses ``SELECT`` to determine if there is an existing row to be updated.
The new algorith tries an ``UPDATE`` directly. In some rare cases the
``UPDATE`` of an existing row isn't visible to Django. An example is the
PostgreSQL ``ON UPDATE`` trigger which returns ``NULL``. In such cases the
new algorithm will end up doing an ``INSERT`` even when a row exists in
the database.
Usually there is no need to set this attribute. The default is
``False``.
See :meth:`django.db.models.Model.save()` for more about the old and
new saving algorithm.
``unique_together``
-------------------

20
docs/releases/1.6.txt
View File

@ -138,6 +138,22 @@ A :djadmin:`check` management command was added, enabling you to verify if your
current configuration (currently oriented at settings) is compatible with the
current version of Django.
:meth:`Model.save() <django.db.models.Model.save()>` algorithm changed
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The :meth:`Model.save() <django.db.models.Model.save()>` method now
tries to directly ``UPDATE`` the database if the instance has a primary
key value. Previously ``SELECT`` was performed to determine if ``UPDATE``
or ``INSERT`` were needed. The new algorithm needs only one query for
updating an existing row while the old algorithm needed two. See
:meth:`Model.save() <django.db.models.Model.save()>` for more details.
In some rare cases the database doesn't report that a matching row was
found when doing an ``UPDATE``. An example is the PostgreSQL ``ON UPDATE``
trigger which returns ``NULL``. In such cases it is possible to set
:attr:`django.db.models.Options.select_on_save` flag to force saving to
use the old algorithm.
Minor features
~~~~~~~~~~~~~~
@ -222,10 +238,6 @@ Minor features
* Generic :class:`~django.contrib.gis.db.models.GeometryField` is now editable
with the OpenLayers widget in the admin.
* The :meth:`Model.save() <django.db.models.Model.save()>` will do
``UPDATE`` - if not updated - ``INSERT`` instead of ``SELECT`` - if not
found ``INSERT`` else ``UPDATE`` in case the model's primary key is set.
* The documentation contains a :doc:`deployment checklist
</howto/deployment/checklist>`.

5
tests/basic/models.py
View File

@ -19,6 +19,11 @@ class Article(models.Model):
def __str__(self):
return self.headline
class ArticleSelectOnSave(Article):
class Meta:
proxy = True
select_on_save = True
@python_2_unicode_compatible
class SelfRef(models.Model):
selfref = models.ForeignKey('self', null=True, blank=True,

60
tests/basic/tests.py
View File

@ -5,6 +5,7 @@ import threading
from django.core.exceptions import ObjectDoesNotExist, MultipleObjectsReturned
from django.db import connections, DEFAULT_DB_ALIAS
from django.db import DatabaseError
from django.db.models.fields import Field, FieldDoesNotExist
from django.db.models.manager import BaseManager
from django.db.models.query import QuerySet, EmptyQuerySet, ValuesListQuerySet, MAX_GET_RESULTS
@ -12,7 +13,7 @@ from django.test import TestCase, TransactionTestCase, skipIfDBFeature, skipUnle
from django.utils import six
from django.utils.translation import ugettext_lazy
from .models import Article, SelfRef
from .models import Article, SelfRef, ArticleSelectOnSave
class ModelTest(TestCase):
@ -806,3 +807,60 @@ class ManagerTest(TestCase):
sorted(BaseManager._get_queryset_methods(QuerySet).keys()),
sorted(self.QUERYSET_PROXY_METHODS),
)
class SelectOnSaveTests(TestCase):
def test_select_on_save(self):
a1 = Article.objects.create(pub_date=datetime.now())
with self.assertNumQueries(1):
a1.save()
asos = ArticleSelectOnSave.objects.create(pub_date=datetime.now())
with self.assertNumQueries(2):
asos.save()
with self.assertNumQueries(1):
asos.save(force_update=True)
Article.objects.all().delete()
with self.assertRaises(DatabaseError):
with self.assertNumQueries(1):
asos.save(force_update=True)
def test_select_on_save_lying_update(self):
"""
Test that select_on_save works correctly if the database
doesn't return correct information about matched rows from
UPDATE.
"""
# Change the manager to not return "row matched" for update().
# We are going to change the Article's _base_manager class
# dynamically. This is a bit of a hack, but it seems hard to
# test this properly otherwise. Article's manager, because
# proxy models use their parent model's _base_manager.
orig_class = Article._base_manager.__class__
class FakeQuerySet(QuerySet):
# Make sure the _update method below is in fact called.
called = False
def _update(self, *args, **kwargs):
FakeQuerySet.called = True
super(FakeQuerySet, self)._update(*args, **kwargs)
return 0
class FakeManager(orig_class):
def get_queryset(self):
return FakeQuerySet(self.model)
try:
Article._base_manager.__class__ = FakeManager
asos = ArticleSelectOnSave.objects.create(pub_date=datetime.now())
with self.assertNumQueries(2):
asos.save()
self.assertTrue(FakeQuerySet.called)
# This is not wanted behaviour, but this is how Django has always
# behaved for databases that do not return correct information
# about matched rows for UPDATE.
with self.assertRaises(DatabaseError):
asos.save(force_update=True)
with self.assertRaises(DatabaseError):
asos.save(update_fields=['pub_date'])
finally:
Article._base_manager.__class__ = orig_class