[1.10.x] Doc'd that model instances with pk=None don't compare equal.

Backport of 224fe22bf1628c1feff110ce993dcb33880bf3a3 from master

1 files changed, 13 insertions, 4 deletions

diff --git a/docs/ref/models/instances.txt b/docs/ref/models/instances.txt
index 49f7184279..e799d0078c 100644
--- a/docs/ref/models/instances.txt
+++ b/docs/ref/models/instances.txt
@@ -646,9 +646,10 @@ with :func:`~django.utils.encoding.python_2_unicode_compatible` as shown above.
 .. method:: Model.__eq__()
 
 The equality method is defined such that instances with the same primary
-key value and the same concrete class are considered equal. For proxy
-models, concrete class is defined as the model's first non-proxy parent;
-for all other models it is simply the model's class.
+key value and the same concrete class are considered equal, except that
+instances with a primary key value of ``None`` aren't equal to anything except
+themselves. For proxy models, concrete class is defined as the model's first
+non-proxy parent; for all other models it's simply the model's class.
 
 For example::
 
@@ -664,10 +665,18 @@ For example::
     class MultitableInherited(MyModel):
         pass
 
+    # Primary keys compared
     MyModel(id=1) == MyModel(id=1)
+    MyModel(id=1) != MyModel(id=2)
+    # Primay keys are None
+    MyModel(id=None) != MyModel(id=None)
+    # Same instance
+    instance = MyModel(id=None)
+    instance == instance
+    # Proxy model
     MyModel(id=1) == MyProxyModel(id=1)
+    # Multi-table inheritance
     MyModel(id=1) != MultitableInherited(id=1)
-    MyModel(id=1) != MyModel(id=2)
 
 ``__hash__()``
 --------------