id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
1463	[patch] [magic-removal] Return None when accessing a non-existent relation entry	Malcolm Tredinnick <malcolm@…>	Adrian Holovaty	"I initially mentioned this problem in http://groups.google.com/group/django-developers/browse_frm/thread/4fb78d1de053249a/ . It is currently impossible to tell if the other end of a !ForeignKey field exists without either constructing a try...except block or using the not-recommended (according to the docs) ''fieldname''_id attribute.

The attached patch changes the behaviour to return None if there is no related entry, rather than raising an exception. It also updates the tests to match this change. User code now changes as follows:

'''old'''
{{{
#!python
if self.parent_id:   # Not recommended for use in docs/model-api.txt. Magic attribute.
    my_parent = self.parent.name
else:
    my_parent = ''

try:
    my_parent = self.parent.name
except DoesNotExist:
    my_parent = ''
}}}

'''new'''
{{{
#!python
if self.parent:
   my_parent = self.parent.name
else:
   my_parent = ''
}}}

I realise this change may be viewed as ""too much effort for no real gain"", so I won't be completely heart-broken if a credible developer closes it as ''wontfix''. But using try...except blocks for standard code paths (which is the case here, when you can have empty relations, such as in a hierarchy) or forcing the use of a magically created attribute (''parent_id'' in the above case), both feel more awkward to me. The relation does not exist, so using None as the related object feels more natural. (ok... getting off the soapbox now...)"	defect	closed	Core (Other)	magic-removal	normal	fixed			Unreviewed	1	0	0	0	0	0