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Ticket #4102 - Allow UPDATE of only specific fields in model.save()

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commit 5671df423bd1bc99c92ebaf05d87babc51faf868 1 parent 80c0cbf
@niwinz niwinz authored
View
47 django/db/models/base.py
@@ -2,6 +2,7 @@
import sys
from functools import update_wrapper
from itertools import izip
+from sets import ImmutableSet
import django.db.models.manager # Imported to register signal handler.
from django.conf import settings
@@ -11,7 +12,7 @@
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 +450,7 @@ def serializable_value(self, field_name):
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 +459,29 @@ def save(self, force_insert=False, force_update=False, using=None):
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 = ImmutableSet(update_fields)
+
+ field_names = set(self._meta.get_all_field_names())
+ not_model_fields = update_fields.difference(field_names)
+ if not_model_fields:
+ raise ValueError("The following fields do not exist in this model: %s"
+ % ', '.join(not_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 +489,8 @@ def save_base(self, raw=False, cls=None, origin=None, force_insert=False,
('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 not update_fields or len(update_fields) > 0
if cls is None:
cls = self.__class__
meta = cls._meta
@@ -483,7 +500,8 @@ def save_base(self, raw=False, cls=None, origin=None, force_insert=False,
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 +521,7 @@ def save_base(self, raw=False, cls=None, origin=None, force_insert=False,
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))
@@ -513,6 +531,9 @@ def save_base(self, raw=False, cls=None, origin=None, force_insert=False,
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
@@ -520,7 +541,7 @@ def save_base(self, raw=False, cls=None, origin=None, force_insert=False,
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
+ 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:
@@ -529,6 +550,8 @@ def save_base(self, raw=False, cls=None, origin=None, force_insert=False,
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 +564,7 @@ def save_base(self, raw=False, cls=None, origin=None, force_insert=False,
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 +584,8 @@ def save_base(self, raw=False, cls=None, origin=None, force_insert=False,
# 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
View
4 django/db/models/signals.py
@@ -5,8 +5,8 @@
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"])
View
21 docs/ref/models/instances.txt
@@ -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.
@@ -334,6 +334,25 @@ 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 as keyword argument
+``update_fields``, only the fields named in that list will be saved to the
+database. This may be desirable if you want to update just one or a few fields
+on an object, as 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
+not None, but empty ``update_fields`` skips the save completely (no signals
+sent). Specifying ``update_fields`` will force an update.
+
Deleting objects
================
View
8 docs/ref/signals.txt
@@ -123,6 +123,10 @@ Arguments sent with this signal:
``using``
The database alias being used.
+``update_fields``
+ List or tuple of fields to update explicitly specified in the ``save()`` method.
+ ``None`` if you do not use this parameter when you call ``save()``.
+
post_save
---------
@@ -154,6 +158,10 @@ Arguments sent with this signal:
``using``
The database alias being used.
+``update_fields``
+ List or tuple of fields to update explicitly specified in the ``save()`` method.
+ ``None`` if you do not use this parameter when you call ``save()``.
+
pre_delete
----------
View
4 docs/releases/1.5.txt
@@ -44,6 +44,10 @@ Django 1.5 also includes several smaller improvements worth noting:
* :mod:`django.utils.timezone` provides a helper for converting aware
datetimes between time zones. See :func:`~django.utils.timezone.localtime`.
+* :meth:`Model.save() <django.db.models.Model.save()>` has a new argument
+ ``update_fields``. Using this argument allows restricting the set of fields
+ to update when saving model instances.
+
Backwards incompatible changes in 1.5
=====================================
View
3  tests/modeltests/update_only_fields/__init__.py
@@ -0,0 +1,3 @@
+# -*- coding: utf-8 -*-
+
+
View
26 tests/modeltests/update_only_fields/models.py
@@ -0,0 +1,26 @@
+
+from django.db import models
+
+GENDER_CHOICES = (
+ ('M', 'Male'),
+ ('F', 'Female'),
+)
+
+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)
+
+
+class Profile(models.Model):
+ name = models.CharField(max_length=200)
+ salary = models.FloatField(default=1000.0)
+
+ def __unicode__(self):
+ return self.name
View
108 tests/modeltests/update_only_fields/tests.py
@@ -0,0 +1,108 @@
+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, Profile
+
+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_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_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'])
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