No longer allow trying to get tags for an unsaved instance. Running the test…

No longer allow trying to get tags for an unsaved instance.  Running the test suite now requires python 2.5 (I'll roll this back if it affects anyone unduely).

taggit/managers.py

@@ -39,6 +39,9 @@ class TaggableManager(object):
         manager.model = type
         if instance is None:
             manager.object_id = None
+        elif instance.pk is None:
+            raise ValueError("%s objects need to have a primary key value "
+                "before you can access their tags." % type.__name__)
         else:
             manager.object_id = instance.pk
         return manager
@@ -86,7 +89,9 @@ class TaggableManager(object):
         return form_class(**kwargs)
 
     def value_from_object(self, instance):
-        return ", ".join(map(unicode, getattr(instance, self.name).all()))
+        if instance.pk:
+            return ", ".join(map(unicode, getattr(instance, self.name).all()))
+        return ""
 
     def related_query_name(self):
         return None

taggit/tests/tests.py

+from __future__ import with_statement
+from contextlib import contextmanager
+
 from django.test import TestCase
 
 from taggit.models import Tag
@@ -12,7 +15,17 @@ class BaseTaggingTest(TestCase):
             got.sort()
             tags.sort()
         self.assertEqual(got, tags)
-
+    
+    @contextmanager
+    def assert_raises(self, exc_type):
+        try:
+            yield
+        except Exception, e:
+            self.assert_(type(e) is exc_type, "%s didn't match expected "
+                "exception type %s" % (e, exc_type))
+        else:
+            self.fail("No exception raised, expected %s" % exc_type)
+    
 
 class AddTagTestCase(BaseTaggingTest):
     def test_add_tag(self):
@@ -44,6 +57,10 @@ class AddTagTestCase(BaseTaggingTest):
         
         apple.delete()
         self.assert_tags_equal(Food.tags.all(), ["green"])
+        
+        f = Food()
+        with self.assert_raises(ValueError):
+            f.tags.all()
 
 
 class LookupByTagTestCase(BaseTaggingTest):