[1.2.X] Fixed #15062 -- Documented the fact that managers must be able to be shallow copied. Thanks to Ian Clelland for the report, and Łukasz Rekucki for the help diagnosing the problem.

Backport of r15220 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@15221 bcc190cf-cafb-0310-a4f2-bffc1f526a37
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Russell Keith-Magee 2011-01-16 06:45:35 +00:00
parent 84db894f44
commit 73b3611723
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@ -274,6 +274,28 @@ it into the inheritance hierarchy *after* the defaults::
# Default manager is CustomManager, but OtherManager is
# also available via the "extra_manager" attribute.
Implementation concerns
-----------------------
Whatever features you add to your custom ``Manager``, it must be
possible to make a shallow copy of a ``Manager`` instance; i.e., the
following code must work::
>>> import copy
>>> manager = MyManager()
>>> my_copy = copy.copy(manager)
Django makes shallow copies of manager objects during certain queries;
if your Manager cannot be copied, those queries will fail.
This won't be an issue for most custom managers. If you are just
adding simple methods to your ``Manager``, it is unlikely that you
will inadvertently make instances of your ``Manager`` uncopyable.
However, if you're overriding ``__getattr__`` or some other private
method of your ``Manager`` object that controls object state, you
should ensure that you don't affect the ability of your ``Manager`` to
be copied.
.. _manager-types:
Controlling automatic Manager types