Upgrade to 0.8.0 'unknown output field'

[snewcomer]

Cannot resolve unknown expression type, unknown output field

Any thoughts on what I am missing in my app? I see a utils.py file was added, but having trouble tracing down the problem.
I'm on the latest Django & django filter, and rest framework packages. Any thoughts on what I am missing b/w the jump from 0.7 to 0.8?

class PersonFilter(FilterSet):

    full_name = AllLookupsFilter(name='full_name')

    class Meta:
        model = Person


class PersonViewSet(viewsets.ModelViewSet):

    resource_name = 'people'
    model = Person
    queryset = Person.objects.all()
    filter_class = PersonFilter
    permission_classes = (permissions.IsAuthenticated,)
    serializer_class = ps.PersonListSerializer 
    filter_backends = (backends.DjangoFilterBackend, filters.SearchFilter,)
    search_fields = ('username', 'first_name', 'last_name', 'title', 'status__name')

[rpkilby]

Hi @snewcomer - is full_name computed or a queryset annotation? Could you provide a more complete example of the model and manager classes?

[snewcomer]

full_name is a field on the model

class PersonQuerySet(models.query.QuerySet):
    pass


class PersonManager(UserManager):
    def get_queryset(self):
        return PersonQuerySet(self.model, using=self._db).filter(deleted__isnull=True)


class Person(AbstractUser, BaseModel):
    title = models.CharField(max_length=50, blank=True, null=True)
    full_name = models.CharField(max_length=50, blank=True)
    status = models.ForeignKey(BaseStatus, blank=True, null=True)
    locale = models.ForeignKey(Locale, blank=True, null=True)
    phone_numbers = GenericRelation(PhoneNumber)

    # Managers
    objects = PersonManager()
    objects_all = UserManager()

    class JSONAPIMeta:
        resource_name = 'people'

    class Meta:
        ordering = ('full_name',)

    def save(self, *args, **kwargs):
        self._update_defaults()
        return super(Person, self).save(*args, **kwargs)

    def _update_defaults(self):
        if not self.locale:
            self.locale = Locale.objects.system_default()

[rpkilby]

Hm. stacktrace?

[snewcomer]

lookup(model_field) prints out as person.Person.full_name

Traceback (most recent call last):
File "/Users/snewcomer/Github/test-app/test-app-django/test-app/person/tests/test_views.py", line 30, in setUp
self.response = self.client.get('/api/admin/people')
File "/Users/snewcomer/.virtualenvs/venv/lib/python2.7/site-packages/django/test/client.py", line 503, in get
**extra)
File "/Users/snewcomer/.virtualenvs/venv/lib/python2.7/site-packages/django/test/client.py", line 304, in get
return self.generic('GET', path, secure=secure, **r)
File "/Users/snewcomer/.virtualenvs/venv/lib/python2.7/site-packages/django/test/client.py", line 380, in generic
return self.request(**r)
File "/Users/snewcomer/.virtualenvs/venv/lib/python2.7/site-packages/django/test/client.py", line 449, in request
response = self.handler(environ)
File "/Users/snewcomer/.virtualenvs/venv/lib/python2.7/site-packages/django/test/client.py", line 123, in __call__
response = self.get_response(request)
File "/Users/snewcomer/.virtualenvs/venv/lib/python2.7/site-packages/django/core/handlers/base.py", line 230, in get_response
response = self.handle_uncaught_exception(request, resolver, sys.exc_info())
File "/Users/snewcomer/.virtualenvs/venv/lib/python2.7/site-packages/django/core/handlers/base.py", line 292, in handle_uncaught_exception
if resolver.urlconf_module is None:
File "/Users/snewcomer/.virtualenvs/venv/lib/python2.7/site-packages/django/utils/functional.py", line 33, in __get__
res = instance.__dict__[self.name] = self.func(instance)
File "/Users/snewcomer/.virtualenvs/venv/lib/python2.7/site-packages/django/core/urlresolvers.py", line 410, in urlconf_module
return import_module(self.urlconf_name)
File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/importlib/__init__.py", line 37, in import_module
__import__(name)
File "/Users/snewcomer/Github/test-app/test-app-django/test-app/test-app/urls.py", line 26, in <module>
from person import import views as person_views
File "/Users/snewcomer/Github/test-app/test-app-django/test-app/person/views.py", line 12, in <module>
class PersonFilter(FilterSet):
File "/Users/snewcomer/.virtualenvs/venv/lib/python2.7/site-packages/rest_framework_filters/filterset.py", line 59, in __new__
for lookup_expr in utils.lookups_for_field(field):
File "/Users/snewcomer/.virtualenvs/venv/lib/python2.7/site-packages/rest_framework_filters/utils.py", line 19, in lookups_for_field
in lookups_for_field(lookup(model_field).output_field)
File "/Users/snewcomer/.virtualenvs/venv/lib/python2.7/site-packages/django/utils/functional.py", line 33, in __get__
res = instance.__dict__[self.name] = self.func(instance)
File "/Users/snewcomer/.virtualenvs/venv/lib/python2.7/site-packages/django/db/models/expressions.py", line 229, in output_field
raise FieldError("Cannot resolve expression type, unknown output_field")
FieldError: Cannot resolve expression type, unknown output_field

[rpkilby]

Thanks - am taking a quick look to see if I can spot anything obvious.

[rpkilby]

Hm, I'll have to dive into this further, but to give you an idea, lookups_for_field is trying to recursively generate all valid lookup expressions for a given field. eg, given a charfield instance, you would get lookups such as exact, iexact, contains, icontains, etc... For a datetime, you would also have transformed lookups such as year__gte.

[rpkilby]

Hi @snewcomer, I tried to recreate this but had to make a few modifications.

• Simplified PersonManager.get_queryset() as there is no deleted field to filter on.
• Commented out ForeignKeys to unprovided models (Status, Locale, PhoneNumber)
• Commented out additional NewPerson model attributes and methods.

The test branch is here, but I was unable to recreate any issues. Feel free to submit PRs to that branch or add code comments here.

[rpkilby]

Hi @snewcomer, were you able to resolve this?

[snewcomer]

Been out of town. Hopefully by the end of the week. Sry about that!

[rpkilby]

No worries. Just ping back when you have new info. Thanks.

[snewcomer]

It's actually this line....remove it and all is good / tests pass. Any thoughts? Can't get a failing test on your fork...

full_name = AllLookupsFilter(name='full_name')

[rpkilby]

Hm. I'm out of options to try on my end without more information.

• What is BaseModel? I just used models.Model. If they're different, try inheriting from that instead.
• Do other fields have problems? eg, does AllLookupsFilter(name='title') fail in your code?
• Is the code you're working on open source? Would I be able to run your tests?
• The list of lookups should resolve as ['regex', 'startswith', 'search', 'gt', 'gte', 'iregex', 'contains', 'endswith', 'iendswith', 'icontains', 'iexact', 'isnull', 'lt', 'istartswith', 'lte', 'in', 'range', 'exact']

So, instead of

class PersonFilter(FilterSet):
    full_name = AllLookupsFilter(name='full_name')

    class Meta:
        model = Person

try

class PersonFilter(FilterSet):

    class Meta:
        model = Person
        fields = {
            'full_name': ['regex', 'startswith', 'search', 'gt', 'gte', 'iregex', 'contains', 'endswith', 'iendswith', 'icontains', 'iexact', 'isnull', 'lt', 'istartswith', 'lte', 'in', 'range', 'exact'],
        }

Is an exception raised from django-filter instead?

[snewcomer]

Yep that worked. AllLookupsFilter fails in tests and prod.

One of the values from the class_lookups(model_field) is unaccent which is a subclass of the Transform lookup and produces the error. Didn't see that as one of the options from above.
https://github.com/philipn/django-rest-framework-filters/blob/master/rest_framework_filters/utils.py#L15

[rpkilby]

That makes a lot more sense. The list from above is the set of default lookups registered to CharFields. It sounds like unaccent is being registered by a third party (I don't see it in Django's source). Can you get the class path of the transform? What module/app that defines it?

Here's an example of some transforms that Django automatically registers.

[rpkilby]

Side note mostly to myself - the error handling here could be improved. We could try to get the output_field ahead of time, then reraise the FieldError with a message that contains the offending transform's name. That said, Django should probably have a more informative message here.