Merge pull request #4611 from freelawproject/4602-pghistorys-event-ad…

…min-page-for-a-single-object-never-loads

Fix event admin page for pghistory

cl/settings/third_party/pghistory.py

@@ -1,12 +1,13 @@
-# Default pghistory trackers for @pghistory.track()
 import pghistory
+from django.apps import apps
 from pghistory.admin.core import (
     BackFilter,
     EventModelFilter,
     LabelFilter,
     MethodFilter,
     ObjFilter,
 )
+from pghistory.config import admin_model
 
 
 class EventsAdminNoFilters(pghistory.admin.EventsAdmin):
@@ -31,7 +32,21 @@ def get_list_filter(self, request):
 
         return filters
 
+    def get_queryset(self, request):
+        # Run query only when we have a model name and object id in url. e.g.
+        # obj=search.RECAPDocument:372557163
+        if "obj" in request.GET and ":" in request.GET.get("obj", ""):
+            model_name, obj_id = request.GET["obj"].split(":")
+            model_class = apps.get_model(model_name)
+            return admin_model().objects.tracks(
+                model_class.objects.get(id=obj_id)
+            )
+
+        # By default it wont perform any query
+        return admin_model().objects.none()
 
+
+# Default pghistory trackers for @pghistory.track()
 PGHISTORY_DEFAULT_TRACKERS = (
     pghistory.UpdateEvent(
         condition=pghistory.AnyChange(exclude_auto=True), row=pghistory.Old