Definining __len__ on a model object breaks it's serialization

[casbon]

In line 37 of django.core.serializers.python you have:

    def handle_field(self, obj, field):
        value = field._get_val_from_obj(obj)

This calls django.db.models.fields.init line 274:

    def _get_val_from_obj(self, obj):
        if obj:
            return getattr(obj, self.attname)
        else:
            return self.get_default()

Now suppose obj has a len which is returning zero. This means 'if obj' is False, then this method returns the default value rather than the object's value.

Suugested fix is to change 'if obj' to 'if obj is not None'.

[claudep]

Been confronted to the same issue today. On one side, the object can workaround this by defining the __nonzero__ method (see ​http://docs.python.org/reference/datamodel.html#object.__len__). On the other side, the test here is not to know if the object evaluates to True or False, but if it can be queried for the attribute.

What about:

def _get_val_from_obj(self, obj):
    return getattr(obj, self.get_attname(), self.get_default())

[jkocherhans]

(In [12576]) Fixed #12546. Objects with a len that returns 0 can now be serialized. Thanks, casobn for the report and Alex Gaynor for the patch and tests.

[jkocherhans]

(In [12577]) [1.1.X] Fixed #12546. Objects with a len that returns 0 can now be serialized. Thanks, casobn for the report and Alex Gaynor for the patch and tests. Backport of r12576 from trunk.

[jacob]

Milestone 1.2 deleted