models: Manage index from migration 0095 with Django.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

zerver/migrations/0095_index_unread_user_messages.py

@@ -1,4 +1,5 @@
-from django.db import migrations
+from django.db import migrations, models
+from django.db.models import Q
 
 
 class Migration(migrations.Migration):
@@ -8,12 +9,13 @@ class Migration(migrations.Migration):
     ]
 
     operations = [
-        migrations.RunSQL(
+        migrations.AddIndex(
-            """
+            model_name="usermessage",
-            CREATE INDEX zerver_usermessage_unread_message_id
+            index=models.Index(
-                ON zerver_usermessage (user_profile_id, message_id)
+                "user_profile",
-                WHERE (flags & 1) = 0;
+                "message",
-            """,
+                condition=Q(flags__andz=1),
-            reverse_sql="DROP INDEX zerver_usermessage_unread_message_id;",
+                name="zerver_usermessage_unread_message_id",
+            ),
         ),
     ]

zerver/models.py

@@ -3128,6 +3128,12 @@ class UserMessage(AbstractUserMessage):
 
     class Meta(AbstractUserMessage.Meta):
         indexes = [
+            models.Index(
+                "user_profile",
+                "message",
+                condition=Q(flags__andz=AbstractUserMessage.flags.read.mask),
+                name="zerver_usermessage_unread_message_id",
+            ),
             models.Index(
                 "user_profile",
                 "message",