Use object instance when getting _meta info in admin

Make sure to use the object instance in admin.py in order to
get the correct app_label and model_name. This is important
when a subclass (e.g. of Newsletter) is used.

Author: frennkie

newsletter/admin.py

@@ -90,7 +90,7 @@ def admin_submissions(self, obj):
 
 class NewsletterAdminLinkMixin(object):
     def admin_newsletter(self, obj):
-        opts = Newsletter._meta
+        opts = obj._meta
         newsletter = obj.newsletter
         url = reverse('admin:%s_%s_change' % (opts.app_label, opts.model_name),
                       args=(newsletter.id,), current_app=self.admin_site.name)

tests/test_models.py

@@ -0,0 +1,25 @@
+from django.test import TestCase
+
+from newsletter.models import Newsletter
+
+
+class CustomNewsletter(Newsletter):
+    class Meta:
+        app_label = 'name_of_my_app'
+
+
+class ModelTestCase(TestCase):
+    """ Test case for models. """
+
+    def test_newsletter_label_name(self):
+        """ Test that _meta returns correct app_label and model_name. """
+        self.assertEqual(Newsletter._meta.app_label, 'newsletter')
+        self.assertEqual(Newsletter._meta.model_name, 'newsletter')
+
+        obj = Newsletter()
+        self.assertEqual(obj._meta.app_label, 'newsletter')
+        self.assertEqual(obj._meta.model_name, 'newsletter')
+
+        custom_obj = CustomNewsletter()
+        self.assertEqual(custom_obj._meta.app_label, 'name_of_my_app')
+        self.assertEqual(custom_obj._meta.model_name, 'customnewsletter')