Rework MethodFilter to works across relationships

Author: Ryan P Kilby

rest_framework_filters/filters.py

@@ -87,3 +87,47 @@ class InSetNumberFilter(InSetFilterBase, NumberFilter):
 
 class InSetCharFilter(InSetFilterBase, NumberFilter):
     field_class = fields.ArrayCharField
+
+
+class MethodFilter(Filter):
+    """
+    This filter will allow you to run a method that exists on the filterset class
+    """
+
+    def __init__(self, *args, **kwargs):
+        self.action = kwargs.pop('action', '')
+        super(MethodFilter, self).__init__(*args, **kwargs)
+
+    def resolve_action(self):
+        """
+        This method provides a hook for the parent FilterSet to resolve the filter's
+        action after initialization. This is necessary, as the filter name may change
+        as it's expanded across related filtersets.
+
+        ie, `is_published` might become `post__is_published`.
+        """
+        # noop if a function was provided as the action
+        if callable(self.action):
+            return
+
+        # otherwise, action is a string representing an action to be called on
+        # the parent FilterSet.
+        parent_action = self.action or 'filter_{0}'.format(self.name)
+
+        parent = getattr(self, 'parent', None)
+        self.action = getattr(parent, parent_action, None)
+
+        assert callable(self.action), (
+            'Expected parent FilterSet `%s.%s` to have a `.%s()` method.' %
+            (parent.__class__.__module__, parent.__class__.__name__, parent_action)
+        )
+
+    def filter(self, qs, value):
+        """
+        This filter method will act as a proxy for the actual method we want to
+        call.
+        It will try to find the method on the parent filterset,
+        if not it attempts to search for the method `field_{{attribute_name}}`.
+        Otherwise it defaults to just returning the queryset.
+        """
+        return self.action(self.name, qs, value)

rest_framework_filters/filterset.py

@@ -74,6 +74,9 @@ def __init__(self, *args, **kwargs):
                 if isnull not in self.filters:
                     self.filters[isnull] = filters.BooleanFilter(name=isnull)
 
+            elif isinstance(filter_, filters.MethodFilter):
+                filter_.resolve_action()
+
     def get_filters(self):
         """
         Build a set of filters based on the requested data. The resulting set

tests/filters.py

@@ -1,7 +1,7 @@
 
 from rest_framework_filters import filters
 from rest_framework_filters.filters import RelatedFilter, AllLookupsFilter
-from rest_framework_filters.filterset import FilterSet
+from rest_framework_filters.filterset import FilterSet, LOOKUP_SEP
 
 
 from .models import (
@@ -63,6 +63,32 @@ class Meta:
         model = Post
 
 
+class PostFilterWithMethod(FilterSet):
+    note = RelatedFilter(NoteFilterWithRelatedAll, name='note')
+    is_published = filters.MethodFilter()
+
+    class Meta:
+        model = Post
+
+    def filter_is_published(self, name, qs, value):
+        null = value.lower() != 'true'
+
+        # 'post', 'is_published'
+        name, _ = name.rsplit(LOOKUP_SEP, 1)
+
+        return qs.filter(**{
+            LOOKUP_SEP.join([name, 'date_published__isnull']): null
+        })
+
+
+class CoverFilterWithRelatedMethodFilter(FilterSet):
+    comment = filters.CharFilter(name='comment')
+    post = RelatedFilter(PostFilterWithMethod, name='post')
+
+    class Meta:
+        model = Cover
+
+
 class CoverFilterWithRelated(FilterSet):
     comment = filters.CharFilter(name='comment')
     post = RelatedFilter(PostFilterWithRelated, name='post')

tests/models.py

@@ -12,6 +12,7 @@ class Note(models.Model):
 class Post(models.Model):
     note = models.ForeignKey(Note)
     content = models.TextField()
+    date_published = models.DateField(null=True)
 
 
 class Cover(models.Model):

tests/test_filterset.py

@@ -22,6 +22,8 @@
     NoteFilterWithRelatedAll,
     NoteFilterWithRelatedAllDifferentFilterName,
     PostFilterWithRelated,
+    # PostFilterWithMethod,
+    CoverFilterWithRelatedMethodFilter,
     CoverFilterWithRelated,
     # PageFilterWithRelated,
     TagFilter,
@@ -324,6 +326,44 @@ def test_get_filterset_subset(self):
         self.assertEqual(len(filterset_class.base_filters), 1)
 
 
+class MethodFilterTests(TestCase):
+
+    if django.VERSION >= (1, 8):
+        @classmethod
+        def setUpTestData(cls):
+            cls.generateTestData()
+
+    else:
+        def setUp(self):
+            self.generateTestData()
+
+    @classmethod
+    def generateTestData(cls):
+        user = User.objects.create(username="user1", email="user1@example.org")
+
+        note1 = Note.objects.create(title="Test 1", content="Test content 1", author=user)
+        note2 = Note.objects.create(title="Test 2", content="Test content 2", author=user)
+
+        post1 = Post.objects.create(note=note1, content="Test content in post 1")
+        post2 = Post.objects.create(note=note2, content="Test content in post 4", date_published=datetime.date.today())
+
+        Cover.objects.create(post=post1, comment="Cover 1")
+        Cover.objects.create(post=post2, comment="Cover 2")
+
+    def test_related_method_filter(self):
+        """
+        Missing MethodFilter filter methods are silently ignored, returning
+        the unfiltered queryset.
+        """
+        GET = {
+            'post__is_published': 'true'
+        }
+        filterset = CoverFilterWithRelatedMethodFilter(GET, queryset=Cover.objects.all())
+        results = list(filterset)
+        self.assertEqual(len(results), 1)
+        self.assertEqual(results[0].comment, "Cover 2")
+
+
 class DatetimeTests(TestCase):
 
     if django.VERSION >= (1, 8):