Index: docs/ref/models/instances.txt =================================================================== --- docs/ref/models/instances.txt (revision 17853) +++ docs/ref/models/instances.txt (working copy) @@ -135,7 +135,7 @@ 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 +334,19 @@ ` and their :ref:`use in update queries `. +Specifying which fields to save +------------------------------- + +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']) + + Deleting objects ================ Index: django/db/models/base.py =================================================================== --- django/db/models/base.py (revision 17853) +++ django/db/models/base.py (working copy) @@ -449,7 +449,7 @@ 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. @@ -460,12 +460,20 @@ """ if force_insert and force_update: 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: + field_names = self._meta.get_all_field_names() + for field_name in update_fields: + if field_name not in field_names: + raise ValueError("%s field does not exist in this model" % (field_name)) + 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 @@ -503,7 +511,7 @@ 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 +521,9 @@ 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 Index: tests/modeltests/update_only_fields/__init__.py =================================================================== --- tests/modeltests/update_only_fields/__init__.py (revision 0) +++ tests/modeltests/update_only_fields/__init__.py (working copy) @@ -0,0 +1,3 @@ +# -*- coding: utf-8 -*- + + Index: tests/modeltests/update_only_fields/tests.py =================================================================== --- tests/modeltests/update_only_fields/tests.py (revision 0) +++ tests/modeltests/update_only_fields/tests.py (working copy) @@ -0,0 +1,54 @@ +from __future__ import absolute_import +from __future__ import with_statement + +from django.test import TestCase +from .models import Person, Employee, Profile + +class UpdateOnlyFieldsTests(TestCase): + def test_simple_update_fields(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') + + s.delete() + + def test_update_field_with_inherited(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) + + e1.delete() + + def test_update_field_with_incorrect_params(self): + s = Person.objects.create(name='Sara', gender='F') + + with self.assertRaises(ValueError): + s.save(update_fields=['first_name']) + + s.delete() Index: tests/modeltests/update_only_fields/models.py =================================================================== --- tests/modeltests/update_only_fields/models.py (revision 0) +++ tests/modeltests/update_only_fields/models.py (working copy) @@ -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') + + +class Profile(models.Model): + name = models.CharField(max_length=200) + salary = models.FloatField(default=1000.0) + + def __unicode__(self): + return self.name