I guess it’s because both EXTRA_MODEL_FIELDS and strings referencing
classes as ForeignKey positional argument rely on the class_prepared
signal. But with it being only sent once, the ForeignKey doesn't have any
chance to catch the signal in time.
For every other use case other than a self-referencing ForeignKey, either
the model being referenced has been created when the extra ForeignKey is
added and it can be resolved as a class right away, or the ForeignKey will
be able to resolve the class as soon as it send the class_prepared signal.
In the case of a self-referencing extra ForeignKey, the ForeignKey is added
after the class_prepared signal has been fired but can't resolve the string
into a class yet because the model has not finished initializing. So the
ForeignKey connect to the class_prepared signal and wait for the class that
just fired it to fire it "again". In vain.
One solution could be to re-raise the class_prepared signal after extra
fields had been added to a model. To do so, you could change the
add_extra_model_fields function in mezzanine/boot/__init__.py to:
def add_extra_model_fields(sender, **kwargs):
"""
Injects custom fields onto the given sender model as defined
by the ``EXTRA_MODEL_FIELDS`` setting.
"""
model_path = "%s.%s" % (sender.__module__, sender.__name__)
extra_fields = fields.get(model_path, {})
if (extra_fields):
for field_name, field in extra_fields.items():
field.contribute_to_class(sender, field_name)
del fields[model_path]
# re-send the class_prepared signal so self-referencing ForeignKey
can catch up
class_prepared.send(sender=sender)
Le vendredi 20 février 2015 17:44:37 UTC+1, Kacper Kołodziej a écrit :
>
> Hi! I'm trying to create multi-level categories structure. I have added
> ForeignKey to 'self' to BlogCategory. I've tried to do it in some different
> ways: http://pastebin.com/77ex9ehe but none of them works. I always
> receive error on syncdb:
>
> CommandError: One or more models did not validate:
>> blog.blogcategory: 'parent_category' has a relation with model self,
>> which has either not been installed or is abstract.
>>
>
>
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