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