Fixed #26891 -- Fixed lookup registration for ForeignObject.

django/db/models/fields/related.py

 from __future__ import unicode_literals
 
+import inspect
 import warnings
 from functools import partial
 
@@ -17,6 +18,7 @@ from django.utils import six
 from django.utils.deprecation import RemovedInDjango20Warning
 from django.utils.encoding import force_text
 from django.utils.functional import cached_property, curry
+from django.utils.lru_cache import lru_cache
 from django.utils.translation import ugettext_lazy as _
 from django.utils.version import get_docs_version
 
@@ -731,26 +733,13 @@ class ForeignObject(RelatedField):
         pathinfos = [PathInfo(from_opts, opts, (opts.pk,), self.remote_field, not self.unique, False)]
         return pathinfos
 
-    def get_lookup(self, lookup_name):
-        if lookup_name == 'in':
-            return RelatedIn
-        elif lookup_name == 'exact':
-            return RelatedExact
-        elif lookup_name == 'gt':
-            return RelatedGreaterThan
-        elif lookup_name == 'gte':
-            return RelatedGreaterThanOrEqual
-        elif lookup_name == 'lt':
-            return RelatedLessThan
-        elif lookup_name == 'lte':
-            return RelatedLessThanOrEqual
-        elif lookup_name == 'isnull':
-            return RelatedIsNull
-        else:
-            raise TypeError('Related Field got invalid lookup: %s' % lookup_name)
-
-    def get_transform(self, *args, **kwargs):
-        raise NotImplementedError('Relational fields do not support transforms.')
+    @classmethod
+    @lru_cache(maxsize=None)
+    def get_lookups(cls):
+        bases = inspect.getmro(cls)
+        bases = bases[:bases.index(ForeignObject) + 1]
+        class_lookups = [parent.__dict__.get('class_lookups', {}) for parent in bases]
+        return cls.merge_dicts(class_lookups)
 
     def contribute_to_class(self, cls, name, private_only=False, **kwargs):
         super(ForeignObject, self).contribute_to_class(cls, name, private_only=private_only, **kwargs)
@@ -767,6 +756,14 @@ class ForeignObject(RelatedField):
             if self.remote_field.limit_choices_to:
                 cls._meta.related_fkey_lookups.append(self.remote_field.limit_choices_to)
 
+ForeignObject.register_lookup(RelatedIn)
+ForeignObject.register_lookup(RelatedExact)
+ForeignObject.register_lookup(RelatedLessThan)
+ForeignObject.register_lookup(RelatedGreaterThan)
+ForeignObject.register_lookup(RelatedGreaterThanOrEqual)
+ForeignObject.register_lookup(RelatedLessThanOrEqual)
+ForeignObject.register_lookup(RelatedIsNull)
+
 
 class ForeignKey(ForeignObject):
     """

django/db/models/query_utils.py

@@ -13,6 +13,7 @@ from collections import namedtuple
 from django.core.exceptions import FieldDoesNotExist
 from django.db.models.constants import LOOKUP_SEP
 from django.utils import tree
+from django.utils.lru_cache import lru_cache
 
 # PathInfo is used when converting lookups (fk__somecol). The contents
 # describe the relation in Model terms (model Options and Fields for both
@@ -27,6 +28,15 @@ class InvalidQuery(Exception):
     pass
 
 
+def subclasses(cls):
+    yield cls
+    # Python 2 lacks 'yield from', which could replace the inner loop
+    for subclass in cls.__subclasses__():
+        # yield from subclasses(subclass)
+        for item in subclasses(subclass):
+            yield item
+
+
 class QueryWrapper(object):
     """
     A type that indicates the contents are an SQL fragment and the associate
@@ -132,20 +142,16 @@ class DeferredAttribute(object):
 
 
 class RegisterLookupMixin(object):
-    def _get_lookup(self, lookup_name):
-        try:
-            return self.class_lookups[lookup_name]
-        except KeyError:
-            # To allow for inheritance, check parent class' class_lookups.
-            for parent in inspect.getmro(self.__class__):
-                if 'class_lookups' not in parent.__dict__:
-                    continue
-                if lookup_name in parent.class_lookups:
-                    return parent.class_lookups[lookup_name]
-        except AttributeError:
-            # This class didn't have any class_lookups
-            pass
-        return None
+
+    @classmethod
+    def _get_lookup(cls, lookup_name):
+        return cls.get_lookups().get(lookup_name, None)
+
+    @classmethod
+    @lru_cache(maxsize=None)
+    def get_lookups(cls):
+        class_lookups = [parent.__dict__.get('class_lookups', {}) for parent in inspect.getmro(cls)]
+        return cls.merge_dicts(class_lookups)
 
     def get_lookup(self, lookup_name):
         from django.db.models.lookups import Lookup
@@ -165,6 +171,22 @@ class RegisterLookupMixin(object):
             return None
         return found
 
+    @staticmethod
+    def merge_dicts(dicts):
+        """
+        Merge dicts in reverse to preference the order of the original list. e.g.,
+        merge_dicts([a, b]) will preference the keys in 'a' over those in 'b'.
+        """
+        merged = {}
+        for d in reversed(dicts):
+            merged.update(d)
+        return merged
+
+    @classmethod
+    def _clear_cached_lookups(cls):
+        for subclass in subclasses(cls):
+            subclass.get_lookups.cache_clear()
+
     @classmethod
     def register_lookup(cls, lookup, lookup_name=None):
         if lookup_name is None:
@@ -172,6 +194,7 @@ class RegisterLookupMixin(object):
         if 'class_lookups' not in cls.__dict__:
             cls.class_lookups = {}
         cls.class_lookups[lookup_name] = lookup
+        cls._clear_cached_lookups()
         return lookup
 
     @classmethod

tests/custom_lookups/models.py

@@ -13,6 +13,10 @@ class Author(models.Model):
         return self.name
 
 
+class Article(models.Model):
+    author = models.ForeignKey(Author, on_delete=models.CASCADE)
+
+
 @python_2_unicode_compatible
 class MySQLUnixTimestamp(models.Model):
     timestamp = models.PositiveIntegerField()

tests/custom_lookups/tests.py

@@ -10,7 +10,7 @@ from django.db import connection, models
 from django.test import TestCase, override_settings
 from django.utils import timezone
 
-from .models import Author, MySQLUnixTimestamp
+from .models import Article, Author, MySQLUnixTimestamp
 
 
 @contextlib.contextmanager
@@ -319,6 +319,28 @@ class LookupTests(TestCase):
                 baseqs.filter(age__div3__range=(1, 2)),
                 [a1, a2, a4], lambda x: x)
 
+    def test_foreignobject_lookup_registration(self):
+        field = Article._meta.get_field('author')
+
+        with register_lookup(models.ForeignObject, Exactly):
+            self.assertIs(field.get_lookup('exactly'), Exactly)
+
+        # ForeignObject should ignore regular Field lookups
+        with register_lookup(models.Field, Exactly):
+            self.assertIsNone(field.get_lookup('exactly'))
+
+    def test_lookups_caching(self):
+        field = Article._meta.get_field('author')
+
+        # clear and re-cache
+        field.get_lookups.cache_clear()
+        self.assertNotIn('exactly', field.get_lookups())
+
+        # registration should bust the cache
+        with register_lookup(models.ForeignObject, Exactly):
+            # getting the lookups again should re-cache
+            self.assertIn('exactly', field.get_lookups())
+
 
 class BilateralTransformTests(TestCase):