Hi everyone,
I just want to mention here that in django-jsonfield repo proposed solution
to solve this problem on third party side:
https://github.com/dmkoch/django-jsonfield/issues/189. Maybe this is the
better way.
Thanks,
Sergey
2017-06-03 0:02 GMT+03:00 Zack Voase <z...@meat.io>:
> Hi all,
>
> I'm encountering exceptions in a number of popular third-party Django
> libraries when upgrading from 1.8 to 1.11. The code path is typically
> `MyModel.objects.get_or_create(...)`, which causes
> `model._meta._property_names` to be checked (to make sure we're not
> querying/setting a property). The problem is, `_property_names` is
> implemented as follows:
>
> # in django/db/models/options.py:
> def _property_names(self):
> return frozenset({
> attr for attr in
> dir(self.model) if isinstance(getattr(self.model, attr), property)
> })
>
> The problem is when a custom field installs a field descriptor on the
> model class (during `contribute_to_class()`), with a `__get__()` method
> like this:
>
> class SomeFieldDescriptor(object):
> # ...
> def __get__(self, instance, type=None):
> if instance is None:
> raise AttributeError("Can only be accessed via an instance.")
> # ...
>
> Libraries which install such descriptors include [django-fsm](
> https://github.com/kmmbvnr/django-fsm/blob/2d2eaee/django_fsm/__init__.
> py#L225) and [django-jsonfield](https://github.com/dmkoch/django-
> jsonfield/blob/2.0.1/jsonfield/subclassing.py#L35). I think the problem
> is that we can't assume that all results of `dir(model_class)` can be
> accessed via `getattr(model_class, attr)` without exception; indeed, the
> Python docs state (c.f. https://docs.python.org/2/
> library/functions.html#dir):
>
> > Because dir() is supplied primarily as a convenience for use at an
> interactive prompt, it tries to supply an interesting set of names more
> than it tries to supply a rigorously or consistently defined set of names,
> and its detailed behavior may change across releases.
>
> A potential fix would be to adjust the definition of `_property_names`
> like so:
>
> def _property_names(self):
> attrs = []
> for attr in dir(self.model):
> try:
> if isinstance(getattr(self.model, attr), property):
> attrs.append(attr)
> except AttributeError:
> pass
> return frozenset(attrs)
>
> Does this seem like a good solution, or even a problem worth solving?
>
> Thanks!
> -- Zack
>
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