Pass ``/admin/app/model/ID/...`` URLs to the correct admin backend.

Using the ID field, the correct ``ct_id`` parameter can already be
determined.

docs/changelog.rst

@@ -5,6 +5,8 @@ Version 0.5.3 (2013-09-17)
 --------------------------
 
 * Fix TypeError when ``base_form`` was not defined.
+* Fix passing ``/admin/app/model/id/XYZ`` urls to the correct admin backend.
+  There is no need to include a ``?ct_id=..`` field, as the ID already provides enough information.
 
 
 Version 0.5.2 (2013-09-05)

polymorphic/admin.py

@@ -276,11 +276,19 @@ class PolymorphicParentModelAdmin(admin.ModelAdmin):
         """
         ct_id = int(request.GET.get('ct_id', 0))
         if not ct_id:
-            raise Http404("No ct_id parameter, unable to find admin subclass for path '{0}'.".format(path))
+            # See if the path started with an ID.
+            try:
+                pos = path.find('/')
+                object_id = long(path[0:pos])
+            except ValueError:
+                raise Http404("No ct_id parameter, unable to find admin subclass for path '{0}'.".format(path))
+
+            ct_id = self.model.objects.values_list('polymorphic_ctype_id', flat=True).get(pk=object_id)
+
 
         real_admin = self._get_real_admin_by_ct(ct_id)
         resolver = RegexURLResolver('^', real_admin.urls)
-        resolvermatch = resolver.resolve(path)
+        resolvermatch = resolver.resolve(path)  # May raise Resolver404
         if not resolvermatch:
             raise Http404("No match for path '{0}' in admin subclass.".format(path))