Fix #79, add transform recursion prevention

CHANGELOG.rst

@@ -1,6 +1,9 @@
 Unreleased
 ----------
 
+* Fixes #79, enabling compatibility with ``django.contrib.postgres``
+* Adds basic infinite recursion prevention for chainable transforms
+
 v0.8.0
 ------
 

rest_framework_filters/utils.py

@@ -1,7 +1,9 @@
 
 from collections import OrderedDict
 
+import django
 from django.db.models.constants import LOOKUP_SEP
+from django.db.models.expressions import Expression
 from django.db.models.lookups import Transform
 from django.utils import six
 
@@ -13,11 +15,47 @@ def lookups_for_field(model_field):
     lookups = []
 
     for expr, lookup in six.iteritems(class_lookups(model_field)):
+        if issubclass(lookup, Transform) and django.VERSION >= (1, 9):
+            transform = lookup(Expression(model_field))
+            lookups += [
+                LOOKUP_SEP.join([expr, sub_expr]) for sub_expr
+                in lookups_for_transform(transform)
+            ]
+
+        else:
+            lookups.append(expr)
+
+    return lookups
+
+
+def lookups_for_transform(transform):
+    """
+    Generates a list of subsequent lookup expressions for a transform.
+
+    Note:
+    Infinite transform recursion is only prevented when the subsequent and
+    passed in transforms are the same class. For example, the ``Unaccent``
+    transform from ``django.contrib.postgres``.
+    There is no cycle detection across multiple transforms. For example,
+    ``a__b__a__b`` would continue to recurse. However, this is not currently
+    a problem (no builtin transforms exhibit this behavior).
+
+    """
+    lookups = []
+
+    for expr, lookup in six.iteritems(class_lookups(transform.output_field)):
         if issubclass(lookup, Transform):
+
+            # type match indicates recursion.
+            if type(transform) == lookup:
+                continue
+
+            sub_transform = lookup(transform)
             lookups += [
-                LOOKUP_SEP.join([expr, transform]) for transform
-                in lookups_for_field(lookup(model_field).output_field)
+                LOOKUP_SEP.join([expr, sub_expr]) for sub_expr
+                in lookups_for_transform(sub_transform)
             ]
+
         else:
             lookups.append(expr)
 
@@ -28,12 +66,12 @@ def class_lookups(model_field):
     """
     Get a compiled set of class_lookups for a model field.
     """
-    field_class = model_field.__class__
+    field_class = type(model_field)
     class_lookups = OrderedDict()
 
     # traverse MRO in reverse, as this puts standard
     # lookups before subclass transforms/lookups
-    for cls in field_class.mro()[::-1]:
+    for cls in reversed(field_class.mro()):
         if hasattr(cls, 'class_lookups'):
             class_lookups.update(getattr(cls, 'class_lookups'))
 

tests/test_utils.py

@@ -30,6 +30,16 @@ def test_transformed_field(self):
         self.assertIn('date__year__exact', lookups)
 
 
+@unittest.skipIf(django.VERSION < (1, 9), "version does not support transformed lookup expressions")
+class LookupsForTransformTests(TestCase):
+    def test_recursion_prevention(self):
+        model_field = Person._meta.get_field('name')
+        lookups = utils.lookups_for_field(model_field)
+
+        self.assertIn('unaccent__exact', lookups)
+        self.assertNotIn('unaccent__unaccent__exact', lookups)
+
+
 class ClassLookupsTests(TestCase):
     def test_standard_field(self):
         model_field = Person._meta.get_field('name')

tests/testapp/__init__.py

@@ -0,0 +1,2 @@
+
+default_app_config = 'tests.testapp.apps.TestappConfig'

tests/testapp/apps.py

@@ -0,0 +1,13 @@
+
+from django.apps import AppConfig
+from django.db.models import CharField, TextField
+
+from .lookups import Unaccent
+
+
+class TestappConfig(AppConfig):
+    name = 'tests.testapp'
+
+    def ready(self):
+        CharField.register_lookup(Unaccent)
+        TextField.register_lookup(Unaccent)

tests/testapp/lookups.py

@@ -0,0 +1,9 @@
+from django.db.models import Transform
+
+
+# This is a copy of the `Unaccent` transform from `django.contrib.postgres`.
+# This is necessary as the postgres app requires psycopg2 to be installed.
+class Unaccent(Transform):
+    bilateral = True
+    lookup_name = 'unaccent'
+    function = 'UNACCENT'