#18416: Query fails when SimpleLazyObject evaluates to None
-------------------------------------+-------------------------------------
Reporter: bouke | Owner: nobody
Type: Bug | Status: closed
Component: Database layer | Version: 1.4
(models, ORM) | Resolution: wontfix
Severity: Normal | Triage Stage:
Keywords: | Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Comment (by dougvanhorn):
I just bumped into this bug. I'm not going to muck with the status, but I
wanted to document my thoughts in case anyone else wants to take up the
cause on this (I've found it to be a tedious, political process).
The code that raises the exception is this (it's found in most of the
Field types):
{{{
#!python
def get_prep_value(self, value):
if value is None:
return None
return int(value)
}}}
It's the `value is None` that causes the problem.
[http://stackoverflow.com/questions/15399024/does-the-is-operator-use-a
-magic-method-in-python It's an identity test].
If the intent of the if-test is return `None` when the supplied value
equates to `None`, then the if-test should be re-written as `value ==
None`, which would test for equality. The equality test is slower,
though, so you'll likely find argument against using it in this section of
the code. Oddly built objects with __eq__ overloaded might also find
trouble.
So there may not be much to do here, leaving the burden on the user to
figure out what's going on. But I wanted to add some documentation to
this bug for future reference.
----
For what it's worth, I ran into this problem with the following code:
{{{
#!python
try:
agreement = Agreement.objects.get(user=request.user)
except Agreement.DoesNotExist, e:
agreement = Agreement(user=request.user)
}}}
I ended up wrapping the view in the `login_required` method, which makes
the `.user` evaluate to something, preventing the bug. But as stated by
**bouke**, the stack is not very helpful.
--
Ticket URL: <https://code.djangoproject.com/ticket/18416#comment:3>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
--
You received this message because you are subscribed to the Google Groups
"Django updates" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to django-updates+unsubscr...@googlegroups.com.
To post to this group, send email to django-updates@googlegroups.com.
For more options, visit https://groups.google.com/groups/opt_out.
