Add index on source_object_id for 10x performance improvment on orderBy

opentech/apply/activity/migrations/0049_auto_20191112_1227.py

+# Generated by Django 2.1.11 on 2019-11-12 12:27
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('activity', '0048_add_project_transition'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='activity',
+            name='source_object_id',
+            field=models.PositiveIntegerField(blank=True, db_index=True, null=True),
+        ),
+    ]

opentech/apply/activity/models.py

@@ -90,7 +90,7 @@ class Activity(models.Model):
     user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.PROTECT)
 
     source_content_type = models.ForeignKey(ContentType, blank=True, null=True, on_delete=models.CASCADE, related_name='activity_source')
-    source_object_id = models.PositiveIntegerField(blank=True, null=True)
+    source_object_id = models.PositiveIntegerField(blank=True, null=True, db_index=True)
     source = GenericForeignKey('source_content_type', 'source_object_id')
 
     message = models.TextField()