Preload related tags.

taggit/managers.py

+from collections import defaultdict
+
 from django.contrib.contenttypes.models import ContentType
 from django.db import models
 from django.db.models.fields.related import ManyToManyRel
@@ -137,9 +139,26 @@ class _TaggableManager(models.Manager):
 
     @require_instance_manager
     def similar_objects(self):
-        return TaggedItem.objects.values('object_id', 'content_type') \
-            .annotate(models.Count('pk')) \
+        qs = TaggedItem.objects.values('object_id', 'content_type') \
+            .annotate(n=models.Count('pk')) \
             .exclude(object_id=self.object_id) \
             .filter(tag__in=self.all()) \
-            .order_by('-pk__count')
-    
+            .order_by('-n')
+
+        preload = defaultdict(set)
+        for result in qs:
+            preload[result["content_type"]].add(result["object_id"])
+
+        items = {}
+        for ct, obj_ids in preload.iteritems():
+            ct = ContentType.objects.get_for_id(ct)
+            items[ct.pk] = dict((o.pk, o) for o in
+                ct.model_class()._default_manager.filter(pk__in=obj_ids)
+            )
+
+        results = []
+        for result in qs:
+            obj = items[result["content_type"]][result["object_id"]]
+            obj.similar_tags = result["n"]
+            results.append(obj)
+        return results

taggit/tests/tests.py

@@ -90,6 +90,6 @@ class SimilarityByTagTestCase(BaseTaggingTest):
         watermelon = Food.objects.create(name="watermelon")
         watermelon.tags.add("green", "juicy", "large", "sweet")
 
-        self.assertEqual(apple.tags.similar_objects(),
-            [{'pk__count': 3, 'content_type': 13, 'object_id': 6}, {'pk__count': 2, 'content_type': 13, 'object_id': 7}])
-
+        similar_objs = apple.tags.similar_objects()
+        self.assertEqual(similar_objs, [pear, watermelon])
+        self.assertEqual(map(lambda x: x.similar_tags, similar_objs), [3, 2])