fix(order): Add composite unique index on order_item version:item_id

.changeset/upset-mangos-stare.md

@@ -0,0 +1,5 @@
+---
+"@medusajs/order": minor
+---
+
+fix(order): Add composite unique index on order_item version:item_id

packages/modules/order/src/migrations/.snapshot-medusa-order.json

@@ -2005,6 +2005,15 @@
           "unique": false,
           "expression": "CREATE INDEX IF NOT EXISTS \"IDX_order_item_deleted_at\" ON \"order_item\" (\"deleted_at\") WHERE deleted_at IS NOT NULL"
         },
+        {
+          "keyName": "IDX_unique_order_item_version_item_id",
+          "columnNames": [],
+          "composite": false,
+          "constraint": false,
+          "primary": false,
+          "unique": false,
+          "expression": "CREATE UNIQUE INDEX IF NOT EXISTS \"IDX_unique_order_item_version_item_id\" ON \"order_item\" (\"version\", \"item_id\") WHERE deleted_at IS NULL"
+        },
         {
           "keyName": "order_item_pkey",
           "columnNames": [

packages/modules/order/src/migrations/Migration20251130184633.ts

@@ -0,0 +1,13 @@
+import { Migration } from '@mikro-orm/migrations';
+
+export class Migration20251130184633 extends Migration {
+
+  override async up(): Promise<void> {
+    this.addSql(`CREATE UNIQUE INDEX IF NOT EXISTS "IDX_unique_order_item_version_item_id" ON "order_item" ("version", "item_id") WHERE deleted_at IS NULL;`);
+  }
+
+  override async down(): Promise<void> {
+    this.addSql(`drop index if exists "IDX_unique_order_item_version_item_id";`);
+  }
+
+}

packages/modules/order/src/models/order-item.ts

@@ -51,6 +51,12 @@ const _OrderItem = model
       unique: false,
       where: "deleted_at IS NOT NULL",
     },
+    {
+      name: "IDX_unique_order_item_version_item_id",
+      on: ["version", "item_id"],
+      unique: true,
+      where: "deleted_at IS NULL",
+    },
   ])
 
 export const OrderItem = _OrderItem