Remove caching functionality from filter backend.

- The caching may have exhibited some race conditions when used in a
  multi-threaded environment.
- The caching should no longer be necessary, as related filter setup
  should be significantly cheaper (hopefully).

Author: Ryan P Kilby

rest_framework_filters/backends.py

@@ -1,50 +1,7 @@
-from copy import deepcopy
 
 import rest_framework.filters
-from rest_framework.compat import django_filters
-
 from .filterset import FilterSet
 
 
-
 class DjangoFilterBackend(rest_framework.filters.DjangoFilterBackend):
-    """
-    A version of `DjangoFilterBackend` that caches repeated filter classes
-    and uses our FilterSet by default.
-    """
     default_filter_set = FilterSet
-
-    _filter_instance_cache = {}
-
-    def _setup_filter_instance(self, _filter, query_params, queryset=None):
-        _filter.data = query_params or {}
-        _filter.is_bound = query_params is not None
-
-        if hasattr(_filter, '_qs'):
-            del _filter._qs
-        if hasattr(_filter, '_form'):
-            del _filter._form
-        if hasattr(_filter, '_ordering_field'):
-            del _filter._ordering_field
-
-        if queryset is None:
-            queryset = _filter._meta.model._default_manager.all()
-        _filter.queryset = queryset
-        # propagate the model being used through the filters
-        for f in _filter.filters.values():
-            f.model = _filter._meta.model
-
-    def filter_queryset(self, request, queryset, view):
-        filter_class = self.get_filter_class(view, queryset)
-
-        if filter_class:
-            if filter_class in self._filter_instance_cache:
-                _filter = self._filter_instance_cache[filter_class]
-                self._setup_filter_instance(_filter, request.query_params, queryset=queryset)
-            else:
-                _filter = filter_class(request.query_params, queryset=queryset)
-                self._filter_instance_cache[filter_class] = _filter
-
-            return _filter.qs
-
-        return queryset