Attribute Error when using rest_flex_fields.filter_backends.FlexFieldsFilterBackend

[hodossy]

Thanks for this great library, I really love this. I have come across an issue however, when I wanted to use rest_flex_fields.filter_backends.FlexFieldsFilterBackend. When I added it to the configuration of DRF, the following import error occured:

Traceback (most recent call last):
  File "manage.py", line 22, in <module>
    main()
  File "manage.py", line 18, in main
    execute_from_command_line(sys.argv)
  File "d:\workspace\my_project\api\.env\lib\site-packages\django\core\management\__init__.py", line 401, in execute_from_command_line
    utility.execute()
  File "d:\workspace\my_project\api\.env\lib\site-packages\django\core\management\__init__.py", line 377, in execute
    django.setup()
  File "d:\workspace\my_project\api\.env\lib\site-packages\django\__init__.py", line 24, in setup
    apps.populate(settings.INSTALLED_APPS)
  File "d:\workspace\my_project\api\.env\lib\site-packages\django\apps\registry.py", line 114, in populate
    app_config.import_models()
  File "d:\workspace\my_project\api\.env\lib\site-packages\django\apps\config.py", line 211, in import_models
    self.models_module = import_module(models_module_name)
  File "d:\workspace\my_project\api\.env\lib\importlib\__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1006, in _gcd_import
  File "<frozen importlib._bootstrap>", line 983, in _find_and_load
  File "<frozen importlib._bootstrap>", line 967, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 677, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 728, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "d:\workspace\my_project\api\my_app\models.py", line 9, in <module>
    from utils.mixins import ResultsModelMixin, TrackFieldChangesMixin
  File "d:\workspace\my_project\api\utils\mixins\__init__.py", line 4, in <module>
    from .results import ResultsModelMixin, ResultsListViewMixin
  File "d:\workspace\my_project\api\utils\mixins\results\__init__.py", line 2, in <module>
    from .views import ResultsListViewMixin
  File "d:\workspace\my_project\api\utils\mixins\results\views.py", line 5, in <module>
    from rest_framework.generics import get_object_or_404
  File "d:\workspace\my_project\api\.env\lib\site-packages\rest_framework\generics.py", line 24, in <module>
    class GenericAPIView(views.APIView):
  File "d:\workspace\my_project\api\.env\lib\site-packages\rest_framework\generics.py", line 43, in GenericAPIView
    filter_backends = api_settings.DEFAULT_FILTER_BACKENDS
  File "d:\workspace\my_project\api\.env\lib\site-packages\rest_framework\settings.py", line 220, in __getattr__
    val = perform_import(val, attr)
  File "d:\workspace\my_project\api\.env\lib\site-packages\rest_framework\settings.py", line 168, in perform_import
    return [import_from_string(item, setting_name) for item in val]
  File "d:\workspace\my_project\api\.env\lib\site-packages\rest_framework\settings.py", line 168, in <listcomp>
    return [import_from_string(item, setting_name) for item in val]
  File "d:\workspace\my_project\api\.env\lib\site-packages\rest_framework\settings.py", line 177, in import_from_string
    return import_string(val)
  File "d:\workspace\my_project\api\.env\lib\site-packages\django\utils\module_loading.py", line 17, in import_string
    module = import_module(module_path)
  File "d:\workspace\my_project\api\.env\lib\importlib\__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "d:\workspace\my_project\api\.env\lib\site-packages\rest_flex_fields\__init__.py", line 3, in <module>
    from .views import FlexFieldsModelViewSet
  File "d:\workspace\my_project\api\.env\lib\site-packages\rest_flex_fields\views.py", line 6, in <module>
    from rest_framework import viewsets
  File "d:\workspace\my_project\api\.env\lib\site-packages\rest_framework\viewsets.py", line 199, in <module>
    class GenericViewSet(ViewSetMixin, generics.GenericAPIView):
AttributeError: module 'rest_framework.generics' has no attribute 'GenericAPIView'

Removing the imports from .views import FlexFieldsModelViewSet from __init__.py and from rest_framework.viewsets import GenericViewSet from filter_backends.py solved the issue for me. Probably the later could be placed behind the TYPE_CHECKING flag from typing, but I have no idea about the first one.

Env:

Django==3.0.7
django-filter==2.3.0
djangorestframework==3.11.0
drf-flex-fields==0.8.5

[hodossy]

I will try to prepare a PR for this one.

[wolph]

While I don't have a proper fix for the issue, you can work around it by manually specifying the filter backend:

import rest_flex_fields.filter_backends as flex_filters
from rest_framework import viewsets


class ModelViewSet(viewsets.ModelViewSet):
    filter_backends = viewsets.ModelViewSet.filter_backends + [
        flex_filters.FlexFieldsFilterBackend,
    ]

[wolph]

I think this might be a duplicate of issue #46

[by-Exist]

I solved the problem by importing FlexFieldsFilterBackend directly from the settings.py module and inserting it into the backend settings.
However, I decided not to use that library due to the Schema format incompatible with drf_spectacular.