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Fixed #4102 -- Allow update of specific fields in model.save() 

Added the ability to update only part of the model's fields in
model.save() by introducing a new kwarg "update_fields". Thanks
to all the numerous reviewers and commenters in the ticket
This commit is contained in:
Andrei Antoukh 2012-05-12 10:24:20 +03:00 committed by Anssi Kääriäinen
parent 25128856f5
commit 365853da01
8 changed files with 272 additions and 17 deletions
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55
django/db/models/base.py
View File

@ -11,7 +11,7 @@ from django.core import validators
from django.db.models.fields import AutoField, FieldDoesNotExist
from django.db.models.fields.related import (ManyToOneRel,
OneToOneField, add_lazy_relation)
from django.db import (connections, router, transaction, DatabaseError,
from django.db import (router, transaction, DatabaseError,
DEFAULT_DB_ALIAS)
from django.db.models.query import Q
from django.db.models.query_utils import DeferredAttribute
@ -449,7 +449,8 @@ class Model(object):
return getattr(self, field_name)
return getattr(self, field.attname)
def save(self, force_insert=False, force_update=False, using=None):
def save(self, force_insert=False, force_update=False, using=None,
update_fields=None):
"""
Saves the current instance. Override this in a subclass if you want to
control the saving process.
@ -458,14 +459,32 @@ class Model(object):
that the "save" must be an SQL insert or update (or equivalent for
non-SQL backends), respectively. Normally, they should not be set.
"""
if force_insert and force_update:
if force_insert and (force_update or update_fields):
raise ValueError("Cannot force both insert and updating in model saving.")
self.save_base(using=using, force_insert=force_insert, force_update=force_update)
if update_fields is not None:
# If update_fields is empty, skip the save. We do also check for
# no-op saves later on for inheritance cases. This bailout is
# still needed for skipping signal sending.
if len(update_fields) == 0:
return
update_fields = frozenset(update_fields)
field_names = set([field.name for field in self._meta.fields
if not field.primary_key])
non_model_fields = update_fields.difference(field_names)
if non_model_fields:
raise ValueError("The following fields do not exist in this "
"model or are m2m fields: %s"
% ', '.join(non_model_fields))
self.save_base(using=using, force_insert=force_insert,
force_update=force_update, update_fields=update_fields)
save.alters_data = True
def save_base(self, raw=False, cls=None, origin=None, force_insert=False,
force_update=False, using=None):
force_update=False, using=None, update_fields=None):
"""
Does the heavy-lifting involved in saving. Subclasses shouldn't need to
override this method. It's separate from save() in order to hide the
@ -473,7 +492,8 @@ class Model(object):
('raw', 'cls', and 'origin').
"""
using = using or router.db_for_write(self.__class__, instance=self)
assert not (force_insert and force_update)
assert not (force_insert and (force_update or update_fields))
assert update_fields is None or len(update_fields) > 0
if cls is None:
cls = self.__class__
meta = cls._meta
@ -483,7 +503,8 @@ class Model(object):
meta = cls._meta
if origin and not meta.auto_created:
signals.pre_save.send(sender=origin, instance=self, raw=raw, using=using)
signals.pre_save.send(sender=origin, instance=self, raw=raw, using=using,
update_fields=update_fields)
# If we are in a raw save, save the object exactly as presented.
# That means that we don't try to be smart about saving attributes
@ -503,7 +524,8 @@ class Model(object):
if field and getattr(self, parent._meta.pk.attname) is None and getattr(self, field.attname) is not None:
setattr(self, parent._meta.pk.attname, getattr(self, field.attname))
self.save_base(cls=parent, origin=org, using=using)
self.save_base(cls=parent, origin=org, using=using,
update_fields=update_fields)
if field:
setattr(self, field.attname, self._get_pk_val(parent._meta))
@ -513,22 +535,27 @@ class Model(object):
if not meta.proxy:
non_pks = [f for f in meta.local_fields if not f.primary_key]
if update_fields:
non_pks = [f for f in non_pks if f.name in update_fields]
# First, try an UPDATE. If that doesn't update anything, do an INSERT.
pk_val = self._get_pk_val(meta)
pk_set = pk_val is not None
record_exists = True
manager = cls._base_manager
if pk_set:
# Determine whether a record with the primary key already exists.
if (force_update or (not force_insert and
# Determine if we should do an update (pk already exists, forced update,
# no force_insert)
if ((force_update or update_fields) or (not force_insert and
manager.using(using).filter(pk=pk_val).exists())):
# It does already exist, so do an UPDATE.
if force_update or non_pks:
values = [(f, None, (raw and getattr(self, f.attname) or f.pre_save(self, False))) for f in non_pks]
if values:
rows = manager.using(using).filter(pk=pk_val)._update(values)
if force_update and not rows:
raise DatabaseError("Forced update did not affect any rows.")
if update_fields and not rows:
raise DatabaseError("Save with update_fields did not affect any rows.")
else:
record_exists = False
if not pk_set or not record_exists:
@ -541,7 +568,7 @@ class Model(object):
fields = meta.local_fields
if not pk_set:
if force_update:
if force_update or update_fields:
raise ValueError("Cannot force an update in save() with no primary key.")
fields = [f for f in fields if not isinstance(f, AutoField)]
@ -561,8 +588,8 @@ class Model(object):
# Signal that the save is complete
if origin and not meta.auto_created:
signals.post_save.send(sender=origin, instance=self,
created=(not record_exists), raw=raw, using=using)
signals.post_save.send(sender=origin, instance=self, created=(not record_exists),
update_fields=update_fields, raw=raw, using=using)
save_base.alters_data = True

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

@ -5,8 +5,8 @@ class_prepared = Signal(providing_args=["class"])
pre_init = Signal(providing_args=["instance", "args", "kwargs"])
post_init = Signal(providing_args=["instance"])
pre_save = Signal(providing_args=["instance", "raw", "using"])
post_save = Signal(providing_args=["instance", "raw", "created", "using"])
pre_save = Signal(providing_args=["instance", "raw", "using", "update_fields"])
post_save = Signal(providing_args=["instance", "raw", "created", "using", "update_fields"])
pre_delete = Signal(providing_args=["instance", "using"])
post_delete = Signal(providing_args=["instance", "using"])

24
docs/ref/models/instances.txt
View File

@ -135,7 +135,7 @@ Saving objects
To save an object back to the database, call ``save()``:
.. method:: Model.save([force_insert=False, force_update=False, using=DEFAULT_DB_ALIAS])
.. method:: Model.save([force_insert=False, force_update=False, using=DEFAULT_DB_ALIAS, update_fields=None])
.. versionadded:: 1.2
The ``using`` argument was added.
@ -289,6 +289,8 @@ almost always do the right thing and trying to override that will lead to
errors that are difficult to track down. This feature is for advanced use
only.
Using ``update_fields`` will force an update similarly to ``force_update``.
Updating attributes based on existing fields
--------------------------------------------
@ -334,6 +336,26 @@ For more details, see the documentation on :ref:`F() expressions
<query-expressions>` and their :ref:`use in update queries
<topics-db-queries-update>`.
Specifying which fields to save
-------------------------------
.. versionadded:: 1.5
If ``save()`` is passed a list of field names in keyword argument
``update_fields``, only the fields named in that list will be updated.
This may be desirable if you want to update just one or a few fields on
an object. There will be a slight performance benefit from preventing
all of the model fields from being updated in the database. For example:
product.name = 'Name changed again'
product.save(update_fields=['name'])
The ``update_fields`` argument can be any iterable containing strings. An
empty ``update_fields`` iterable will skip the save. A value of None will
perform an update on all fields.
Specifying ``update_fields`` will force an update.
Deleting objects
================

12
docs/ref/signals.txt
View File

@ -123,6 +123,12 @@ Arguments sent with this signal:
``using``
The database alias being used.
.. versionadded:: 1.5
``update_fields``
The set of fields to update explicitly specified in the ``save()`` method.
``None`` if this argument was not used in the ``save()`` call.
post_save
---------
@ -154,6 +160,12 @@ Arguments sent with this signal:
``using``
The database alias being used.
.. versionadded:: 1.5
``update_fields``
The set of fields to update explicitly specified in the ``save()`` method.
``None`` if this argument was not used in the ``save()`` call.
pre_delete
----------

11
docs/releases/1.5.txt
View File

@ -33,6 +33,17 @@ version compatible with Python 2.6.
What's new in Django 1.5
========================
Support for saving a subset of model's fields
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The method :meth:`Model.save() <django.db.models.Model.save()>` has a new
keyword argument ``update_fields``. By using this argument it is possible to
save only a select list of model's fields. This can be useful for performance
reasons or when trying to avoid overwriting concurrent changes.
See the :meth:`Model.save() <django.db.models.Model.save()>` documentation for
more details.
Minor features
~~~~~~~~~~~~~~

0
tests/modeltests/update_only_fields/__init__.py Normal file
View File

37
tests/modeltests/update_only_fields/models.py Normal file
View File

@ -0,0 +1,37 @@
from django.db import models
GENDER_CHOICES = (
('M', 'Male'),
('F', 'Female'),
)
class Account(models.Model):
num = models.IntegerField()
class Person(models.Model):
name = models.CharField(max_length=20)
gender = models.CharField(max_length=1, choices=GENDER_CHOICES)
def __unicode__(self):
return self.name
class Employee(Person):
employee_num = models.IntegerField(default=0)
profile = models.ForeignKey('Profile', related_name='profiles', null=True)
accounts = models.ManyToManyField('Account', related_name='employees', blank=True, null=True)
class Profile(models.Model):
name = models.CharField(max_length=200)
salary = models.FloatField(default=1000.0)
def __unicode__(self):
return self.name
class ProxyEmployee(Employee):
class Meta:
proxy = True

146
tests/modeltests/update_only_fields/tests.py Normal file
View File

@ -0,0 +1,146 @@
from __future__ import absolute_import
from django.test import TestCase
from django.db.models.signals import pre_save, post_save
from .models import Person, Employee, ProxyEmployee, Profile, Account
class UpdateOnlyFieldsTests(TestCase):
def test_update_fields_basic(self):
s = Person.objects.create(name='Sara', gender='F')
self.assertEqual(s.gender, 'F')
s.gender = 'M'
s.name = 'Ian'
s.save(update_fields=['name'])
s = Person.objects.get(pk=s.pk)
self.assertEqual(s.gender, 'F')
self.assertEqual(s.name, 'Ian')
def test_update_fields_m2m(self):
profile_boss = Profile.objects.create(name='Boss', salary=3000)
e1 = Employee.objects.create(name='Sara', gender='F',
employee_num=1, profile=profile_boss)
a1 = Account.objects.create(num=1)
a2 = Account.objects.create(num=2)
e1.accounts = [a1,a2]
with self.assertRaises(ValueError):
e1.save(update_fields=['accounts'])
def test_update_fields_inheritance(self):
profile_boss = Profile.objects.create(name='Boss', salary=3000)
profile_receptionist = Profile.objects.create(name='Receptionist', salary=1000)
e1 = Employee.objects.create(name='Sara', gender='F',
employee_num=1, profile=profile_boss)
e1.name = 'Ian'
e1.gender = 'M'
e1.save(update_fields=['name'])
e2 = Employee.objects.get(pk=e1.pk)
self.assertEqual(e2.name, 'Ian')
self.assertEqual(e2.gender, 'F')
self.assertEqual(e2.profile, profile_boss)
e2.profile = profile_receptionist
e2.name = 'Sara'
e2.save(update_fields=['profile'])
e3 = Employee.objects.get(pk=e1.pk)
self.assertEqual(e3.name, 'Ian')
self.assertEqual(e3.profile, profile_receptionist)
def test_update_fields_inheritance_with_proxy_model(self):
profile_boss = Profile.objects.create(name='Boss', salary=3000)
profile_receptionist = Profile.objects.create(name='Receptionist', salary=1000)
e1 = ProxyEmployee.objects.create(name='Sara', gender='F',
employee_num=1, profile=profile_boss)
e1.name = 'Ian'
e1.gender = 'M'
e1.save(update_fields=['name'])
e2 = ProxyEmployee.objects.get(pk=e1.pk)
self.assertEqual(e2.name, 'Ian')
self.assertEqual(e2.gender, 'F')
self.assertEqual(e2.profile, profile_boss)
e2.profile = profile_receptionist
e2.name = 'Sara'
e2.save(update_fields=['profile'])
e3 = ProxyEmployee.objects.get(pk=e1.pk)
self.assertEqual(e3.name, 'Ian')
self.assertEqual(e3.profile, profile_receptionist)
def test_update_fields_signals(self):
p = Person.objects.create(name='Sara', gender='F')
pre_save_data = []
def pre_save_receiver(**kwargs):
pre_save_data.append(kwargs['update_fields'])
pre_save.connect(pre_save_receiver)
post_save_data = []
def post_save_receiver(**kwargs):
post_save_data.append(kwargs['update_fields'])
post_save.connect(post_save_receiver)
p.save(update_fields=['name'])
self.assertEqual(len(pre_save_data), 1)
self.assertEqual(len(pre_save_data[0]), 1)
self.assertTrue('name' in pre_save_data[0])
self.assertEqual(len(post_save_data), 1)
self.assertEqual(len(post_save_data[0]), 1)
self.assertTrue('name' in post_save_data[0])
def test_update_fields_incorrect_params(self):
s = Person.objects.create(name='Sara', gender='F')
with self.assertRaises(ValueError):
s.save(update_fields=['first_name'])
with self.assertRaises(ValueError):
s.save(update_fields="name")
def test_empty_update_fields(self):
s = Person.objects.create(name='Sara', gender='F')
pre_save_data = []
def pre_save_receiver(**kwargs):
pre_save_data.append(kwargs['update_fields'])
pre_save.connect(pre_save_receiver)
post_save_data = []
def post_save_receiver(**kwargs):
post_save_data.append(kwargs['update_fields'])
post_save.connect(post_save_receiver)
# Save is skipped.
with self.assertNumQueries(0):
s.save(update_fields=[])
# Signals were skipped, too...
self.assertEqual(len(pre_save_data), 0)
self.assertEqual(len(post_save_data), 0)
def test_num_queries_inheritance(self):
s = Employee.objects.create(name='Sara', gender='F')
s.employee_num = 1
s.name = 'Emily'
with self.assertNumQueries(1):
s.save(update_fields=['employee_num'])
s = Employee.objects.get(pk=s.pk)
self.assertEqual(s.employee_num, 1)
self.assertEqual(s.name, 'Sara')
s.employee_num = 2
s.name = 'Emily'
with self.assertNumQueries(1):
s.save(update_fields=['name'])
s = Employee.objects.get(pk=s.pk)
self.assertEqual(s.name, 'Emily')
self.assertEqual(s.employee_num, 1)
# A little sanity check that we actually did updates...
self.assertEqual(Employee.objects.count(), 1)
self.assertEqual(Person.objects.count(), 1)
with self.assertNumQueries(2):
s.save(update_fields=['name', 'employee_num'])