Fixed #176 -- Disallow multiple TaggableManagers with the same through model.

taggit/managers.py

@@ -130,10 +130,12 @@ class TaggableManager(RelatedField, Field):
             tagged_items = GenericRelation(self.through)
             tagged_items.contribute_to_class(cls, 'tagged_items')
 
-            for rel in cls._meta.local_many_to_many:
-                if isinstance(rel, TaggableManager) and rel.use_gfk and rel != self:
-                    raise ValueError('You can only have one TaggableManager per model'
-                        ' using generic relations.')
+        for rel in cls._meta.local_many_to_many:
+            if rel == self or not isinstance(rel, TaggableManager):
+                continue
+            if rel.through == self.through:
+                raise ValueError('You can\'t have two TaggableManagers with the'
+                                 ' same through model.')
 
     def save_form_data(self, instance, value):
         getattr(instance, self.name).set(*value)

tests/models.py

@@ -21,6 +21,14 @@ class MultipleTags(models.Model):
     tags1 = TaggableManager(through=Through1, related_name='tags1')
     tags2 = TaggableManager(through=Through2, related_name='tags2')
 
+# Ensure that two TaggableManagers with GFK via different through models are allowed.
+class ThroughGFK(GenericTaggedItemBase):
+    tag = models.ForeignKey(Tag, related_name='tagged_items')
+
+class MultipleTagsGFK(models.Model):
+    tags1 = TaggableManager(related_name='tagsgfk1')
+    tags2 = TaggableManager(through=ThroughGFK, related_name='tagsgfk2')
+
 
 @python_2_unicode_compatible
 class Food(models.Model):