models: Manage indexes from migration 0279 with Django.

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

zerver/migrations/0279_message_recipient_subject_indexes.py

@@ -1,6 +1,9 @@
 # Generated by Django 2.2.12 on 2020-04-30 00:35
 
-from django.db import migrations
+from django.contrib.postgres.operations import AddIndexConcurrently
+from django.db import migrations, models
+from django.db.models import F
+from django.db.models.functions import Upper
 
 
 class Migration(migrations.Migration):
@@ -11,14 +14,22 @@ class Migration(migrations.Migration):
     ]
 
     operations = [
-        migrations.RunSQL(
-            """
-        CREATE INDEX CONCURRENTLY IF NOT EXISTS zerver_message_recipient_upper_subject ON zerver_message (recipient_id, upper(subject::text), id DESC NULLS LAST);
-        """
+        AddIndexConcurrently(
+            model_name="message",
+            index=models.Index(
+                "recipient",
+                Upper("subject"),
+                F("id").desc(nulls_last=True),
+                name="zerver_message_recipient_upper_subject",
+            ),
+        ),
+        AddIndexConcurrently(
+            model_name="message",
+            index=models.Index(
+                "recipient",
+                "subject",
+                F("id").desc(nulls_last=True),
+                name="zerver_message_recipient_subject",
             ),
-        migrations.RunSQL(
-            """
-        CREATE INDEX CONCURRENTLY IF NOT EXISTS zerver_message_recipient_subject ON zerver_message (recipient_id, subject, id DESC NULLS LAST);
-        """
         ),
     ]

zerver/models.py

@@ -30,7 +30,8 @@ from django.core.exceptions import ValidationError
 from django.core.validators import MinLengthValidator, RegexValidator, URLValidator, validate_email
 from django.db import models, transaction
 from django.db.backends.base.base import BaseDatabaseWrapper
-from django.db.models import CASCADE, Manager, Q, Sum
+from django.db.models import CASCADE, F, Manager, Q, Sum
+from django.db.models.functions import Upper
 from django.db.models.query import QuerySet
 from django.db.models.signals import post_delete, post_save, pre_delete
 from django.db.models.sql.compiler import SQLCompiler
@@ -2798,6 +2799,22 @@ class Message(AbstractMessage):
             return True
         return False
 
+    class Meta:
+        indexes = [
+            models.Index(
+                "recipient",
+                Upper("subject"),
+                F("id").desc(nulls_last=True),
+                name="zerver_message_recipient_upper_subject",
+            ),
+            models.Index(
+                "recipient",
+                "subject",
+                F("id").desc(nulls_last=True),
+                name="zerver_message_recipient_subject",
+            ),
+        ]
+
 
 def get_context_for_message(message: Message) -> Sequence[Message]:
     # TODO: Change return type to QuerySet[Message]