From c0afa102bb30fcdb3202a2b7745ed039b6aec2b6 Mon Sep 17 00:00:00 2001
From: Cedric Vidal <cedric.vidal@gmail.com>
Date: Thu, 26 Feb 2026 14:55:12 -0800
Subject: [PATCH] fix: bootstrap _migrations indexes before mongo-migrate-ts
 runs
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Cosmos DB (MongoDB API) rejects sort operations on unindexed fields.
mongo-migrate-ts internally does .sort({ timestamp: -1 }) to list
applied migrations. Without a pre-existing index on the _migrations
collection, the migration job fails with BadRequest (400).

This is a chicken-and-egg problem — we cannot use a migration to
create the index because the framework cannot read the collection
without it. The fix pre-creates { timestamp: -1 } and { className: 1 }
indexes on _migrations before handing off to mongoMigrateCli.
---
 packages/db-migrations/src/migrate.ts | 35 ++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/packages/db-migrations/src/migrate.ts b/packages/db-migrations/src/migrate.ts
index 70d5df122..753f8bb51 100644
--- a/packages/db-migrations/src/migrate.ts
+++ b/packages/db-migrations/src/migrate.ts
@@ -16,6 +16,7 @@
  */
 
 import { mongoMigrateCli } from "mongo-migrate-ts";
+import { MongoClient } from "mongodb";
 import { join, dirname } from "node:path";
 import { fileURLToPath } from "node:url";
 
@@ -32,10 +33,42 @@ const database =
   process.env.MONGO_DATABASE ??
   "requests-db";
 
+const MIGRATIONS_COLLECTION = "_migrations";
+
+/**
+ * Bootstrap required indexes on the _migrations collection BEFORE
+ * mongo-migrate-ts runs.
+ *
+ * Cosmos DB (MongoDB API) rejects sort operations on unindexed fields.
+ * mongo-migrate-ts internally does `.sort({ timestamp: -1 })` to list and
+ * find the last applied migration, so this index must exist before the
+ * framework even checks migration status.
+ *
+ * This is a chicken-and-egg issue — we can't use a migration to create
+ * the index because the framework can't read the migrations collection
+ * without it.
+ */
+async function ensureMigrationsCollectionIndexes(): Promise<void> {
+  const client = await MongoClient.connect(uri);
+  try {
+    const db = client.db(database);
+    const col = db.collection(MIGRATIONS_COLLECTION);
+    await col.createIndex({ timestamp: -1 }).catch(() => {});
+    await col.createIndex({ className: 1 }).catch(() => {});
+    console.log(
+      `Ensured indexes on ${MIGRATIONS_COLLECTION} collection`,
+    );
+  } finally {
+    await client.close();
+  }
+}
+
+await ensureMigrationsCollectionIndexes();
+
 mongoMigrateCli({
   uri,
   database,
   migrationsDir: join(__dirname, "migrations"),
-  migrationsCollection: "_migrations",
+  migrationsCollection: MIGRATIONS_COLLECTION,
   globPattern: "**/*.ts",
 });