Handle isnull filters differently (#753)

* Handle isnull filters differently

* Change to rsplit

graphene_django/filter/tests/test_fields.py

@@ -56,8 +56,6 @@ if DJANGO_FILTER_INSTALLED:
             model = Pet
             interfaces = (Node,)
 
-    # schema = Schema()
-
 
 def get_args(field):
     return field.args
@@ -820,6 +818,58 @@ def test_integer_field_filter_type():
     )
 
 
+def test_other_filter_types():
+    class PetType(DjangoObjectType):
+        class Meta:
+            model = Pet
+            interfaces = (Node,)
+            filter_fields = {"age": ["exact", "isnull", "lt"]}
+            fields = ("age",)
+
+    class Query(ObjectType):
+        pets = DjangoFilterConnectionField(PetType)
+
+    schema = Schema(query=Query)
+
+    assert str(schema) == dedent(
+        """\
+        schema {
+          query: Query
+        }
+
+        interface Node {
+          id: ID!
+        }
+
+        type PageInfo {
+          hasNextPage: Boolean!
+          hasPreviousPage: Boolean!
+          startCursor: String
+          endCursor: String
+        }
+
+        type PetType implements Node {
+          age: Int!
+          id: ID!
+        }
+
+        type PetTypeConnection {
+          pageInfo: PageInfo!
+          edges: [PetTypeEdge]!
+        }
+
+        type PetTypeEdge {
+          node: PetType
+          cursor: String!
+        }
+
+        type Query {
+          pets(before: String, after: String, first: Int, last: Int, age: Int, age_Isnull: Boolean, age_Lt: Int): PetTypeConnection
+        }
+    """
+    )
+
+
 def test_filter_filterset_based_on_mixin():
     class ArticleFilterMixin(FilterSet):
         @classmethod

graphene_django/filter/utils.py

@@ -18,9 +18,16 @@ def get_filtering_args_from_filterset(filterset_class, type):
         if name in filterset_class.declared_filters:
             form_field = filter_field.field
         else:
-            field_name = name.split("__", 1)[0]
+            try:
+                field_name, filter_type = name.rsplit("__", 1)
+            except ValueError:
+                field_name = name
+                filter_type = None
 
-            if hasattr(model, field_name):
+            # If the filter type is `isnull` then use the filter provided by
+            # DjangoFilter (a BooleanFilter).
+            # Otherwise try and get a filter based on the actual model field
+            if filter_type != "isnull" and hasattr(model, field_name):
                 model_field = model._meta.get_field(field_name)
 
                 if hasattr(model_field, "formfield"):