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Fixed model.__eq__ and __hash__ for no pk value cases

The __eq__ method now considers two instances without primary key value
equal only when they have same id(). The __hash__ method raises
TypeError for no primary key case.

Fixed #18864, fixed #18250

Thanks to Tim Graham for docs review.
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commit 6af05e7a0f0e4604d6a67899acaa99d73ec0dfaa 1 parent 768bbf3
@akaariai akaariai authored
13 django/db/models/
@@ -459,14 +459,21 @@ def __str__(self):
return '%s object' % self.__class__.__name__
def __eq__(self, other):
- return (isinstance(other, Model) and
- self._meta.concrete_model == other._meta.concrete_model and
- self._get_pk_val() == other._get_pk_val())
+ if not isinstance(other, Model):
+ return False
+ if self._meta.concrete_model != other._meta.concrete_model:
+ return False
+ my_pk = self._get_pk_val()
+ if my_pk is None:
+ return self is other
+ return my_pk == other._get_pk_val()
def __ne__(self, other):
return not self.__eq__(other)
def __hash__(self):
+ if self._get_pk_val() is None:
+ raise TypeError("Model instances without primary key value are unhashable")
return hash(self._get_pk_val())
def __reduce__(self):
6 django/forms/
@@ -631,7 +631,11 @@ def validate_unique(self):
seen_data = set()
for form in valid_forms:
# get data for each field of each of unique_check
- row_data = tuple([form.cleaned_data[field] for field in unique_check if field in form.cleaned_data])
+ row_data = (form.cleaned_data[field]
+ for field in unique_check if field in form.cleaned_data)
+ # Reduce Model instances to their primary key values
+ row_data = tuple(d._get_pk_val() if hasattr(d, '_get_pk_val') else d
+ for d in row_data)
if row_data and not None in row_data:
# if we've already seen it then we have a uniqueness failure
if row_data in seen_data:
19 docs/ref/models/instances.txt
@@ -521,6 +521,25 @@ For example::
In previous versions only instances of the exact same class and same
primary key value were considered equal.
+.. method:: Model.__hash__()
+The ``__hash__`` method is based on the instance's primary key value. It
+is effectively hash( If the instance doesn't have a primary key
+value then a ``TypeError`` will be raised (otherwise the ``__hash__``
+method would return different values before and after the instance is
+saved, but changing the ``__hash__`` value of an instance `is forbidden
+in Python`_).
+.. versionchanged:: 1.7
+ In previous versions instance's without primary key value were
+ hashable.
+.. _is forbidden in Python:
8 docs/releases/1.7.txt
@@ -199,6 +199,14 @@ Miscellaneous
equal when primary keys match. Previously only instances of exact same
class were considered equal on primary key match.
+* The :meth:`django.db.models.Model.__eq__` method has changed such that
+ two ``Model`` instances without primary key values won't be considered
+ equal (unless they are the same instance).
+* The :meth:`django.db.models.Model.__hash__` will now raise ``TypeError``
+ when called on an instance without a primary key value. This is done to
+ avoid mutable ``__hash__`` values in containers.
Features deprecated in 1.7
11 tests/basic/
@@ -708,9 +708,20 @@ def test_ticket_20278(self):
def test_eq(self):
+ self.assertEqual(Article(id=1), Article(id=1))
self.assertNotEqual(Article(id=1), object())
self.assertNotEqual(object(), Article(id=1))
+ a = Article()
+ self.assertEqual(a, a)
+ self.assertNotEqual(Article(), a)
+ def test_hash(self):
+ # Value based on PK
+ self.assertEqual(hash(Article(id=1)), hash(1))
+ with self.assertRaises(TypeError):
+ # No PK value -> unhashable (because save() would then change
+ # hash)
+ hash(Article())
class ConcurrentSaveTests(TransactionTestCase):
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