Make papertrail admin viewer resilient to the model class referenced …

…by the related object not being available

CHANGELOG.rst

@@ -1,3 +1,11 @@
+Version 1.1.3
+===========================================================
+*   Make papertrail admin viewer resilient to the model class referenced
+    by the related object not being available (this would happen, for example,
+    when an app is removed from INSTALLED_APPS but it's Content Type object
+    is still in the database).
+
+
 Version 1.1.2
 ===========================================================
 *   Add default Entry admin

papertrail/__init__.py

@@ -1,2 +1,2 @@
-__version__ = '1.1.2'
+__version__ = '1.1.3'
 default_app_config = 'papertrail.apps.PapertrailConfig'

papertrail/models.py

@@ -240,6 +240,14 @@ class RelatedObject(models.Model):
     class Meta:
         abstract = True
 
+    @property
+    def safe_related_object(self):
+        try:
+            return self.related_object
+        # This will happen if the model class of this object is not available, for example if the app providing it has been removed from INSTALLED_APPS
+        except AttributeError:
+            return None
+
 
 class EntryRelatedObject(RelatedObject):
     entry = models.ForeignKey('Entry', related_name='targets')

papertrail/templates/admin/object_papertrail.html

@@ -77,8 +77,8 @@
                                 <ul>
                                 {% for target in action.targets.all %}
                                     <li>
-                                        <a href="{{ target.related_object|adminview:'change' }}">
-                                            {{ target.relation_name }}: {{ target.related_object }}
+                                        <a href="{{ target.safe_related_object|adminview:'change' }}">
+                                            {{ target.relation_name }}: {{ target.safe_related_object }}
                                         </a>
                                     </li>
                                 {% endfor %}

setup.py

@@ -9,7 +9,7 @@
 
 setup(
     name='django-papertrail',
-    version='1.1.2',
+    version='1.1.3',
     packages=['papertrail'],
     install_requires=[
         'Django>=1.7',