Ticket #4102: update_fields_django-1.4-3.patch

docs/ref/signals.txt

@@ -123 +123 @@
 ``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 +158 @@
 ``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
 ----------
 

docs/ref/models/instances.txt

@@ -135 +135 @@
 
 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 +334 @@
 <query-expressions>` and their :ref:`use in update queries
 <topics-db-queries-update>`.
 
+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'])
+
+
+``update_fields`` must be a list, tuple or None. And this parameter implies ``force_update=True``.
+
+
 Deleting objects
 ================
 

django/db/models/signals.py

@@ -5 +5 @@
 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"])

django/db/models/base.py

@@ -449 +449 @@
             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 +460 @@
         """
         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))
 
+            force_update = True
+
+        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
@@ -483 +493 @@
             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 +514 @@
                 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 +524 @@
         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
@@ -561 +575 @@
 
         # 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

tests/modeltests/update_only_fields/__init__.py

@@ +1 @@
+# -*- coding: utf-8 -*-
+
+

tests/modeltests/update_only_fields/tests.py

@@ +1 @@
+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')
+
+    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)
+
+    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'])

tests/modeltests/update_only_fields/models.py

@@ +1 @@
+
+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