#32524: unexpected behavior when using gettattr for related object
-------------------------------------+-------------------------------------
Reporter: elonzh | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: 3.1
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 1
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Changes (by elonzh):
* needs_docs: 0 => 1
Old description:
> Assuming we have a model like that:
>
> {{{
> class UserProfile(models.Model):
> user = models.OneToOneField(User, related_name="profile",
> on_delete=models.CASCADE)
> ...
> }}}
>
> An user may not have an UserProfile instance so we will use such logic:
>
> {{{
> profile = getattr(request.user, "profile",
> UserProfile(user=request.user))
> }}}
>
> But django will always return the default value no matter
> `request.user.profile` exists or not.
>
> Here is the poc:
>
> {{{
> In [1]: u = User.objects.get(username='s')
>
> In [2]: u.profile
> Out[2]: <UserProfile: UserProfile object (5)>
>
> In [3]: getattr(u, 'profile', UserProfile())
> Out[3]: <UserProfile: UserProfile object (5)>
>
> In [4]: getattr(u, 'profile', UserProfile(user=u))
> Out[4]: <UserProfile: UserProfile object (None)>
>
> }}}
>
> the problem is `UserProfile(user=u)` will update the `User.profile` when
> we init `UserProfile`.
New description:
Assuming we have a model like that:
{{{
class UserProfile(models.Model):
user = models.OneToOneField(User, related_name="profile",
on_delete=models.CASCADE)
...
}}}
An user may not have an UserProfile instance so we will use such logic:
{{{
profile = getattr(request.user, "profile", UserProfile(user=request.user))
}}}
But django will always return the default value no matter
`request.user.profile` exists or not.
Here is the poc:
{{{
In [1]: u = User.objects.get(username='s')
In [2]: u.profile
Out[2]: <UserProfile: UserProfile object (5)>
In [3]: getattr(u, 'profile', UserProfile())
Out[3]: <UserProfile: UserProfile object (5)>
In [4]: getattr(u, 'profile', UserProfile(user=u))
Out[4]: <UserProfile: UserProfile object (None)>
}}}
the problem is `UserProfile(user=u)` will update the `u.profile` when we
init `UserProfile`.
I know this issue is caused by design, maybe we should update the document
for such case.
--
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Ticket URL: <https://code.djangoproject.com/ticket/32524#comment:1>
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