From 11cb025886a83adcf26c4c1f2e6bfec306fc4cb8 Mon Sep 17 00:00:00 2001
From: mijinummi <tech.md.auwal@gmail.com>
Date: Fri, 27 Mar 2026 19:42:26 +0100
Subject: [PATCH] feat(database): implement transaction middleware with ACID
 guarantees, isolation levels, and rollback handling (#322)

---
 .../src/transaction/transaction.logger.ts     | 14 +++++++
 .../src/transaction/transaction.manager.ts    | 36 ++++++++++++++++++
 .../src/transaction/transaction.middleware.ts | 37 +++++++++++++++++++
 3 files changed, 87 insertions(+)
 create mode 100644 middleware/src/transaction/transaction.logger.ts
 create mode 100644 middleware/src/transaction/transaction.manager.ts
 create mode 100644 middleware/src/transaction/transaction.middleware.ts

diff --git a/middleware/src/transaction/transaction.logger.ts b/middleware/src/transaction/transaction.logger.ts
new file mode 100644
index 0000000..2e92309
--- /dev/null
+++ b/middleware/src/transaction/transaction.logger.ts
@@ -0,0 +1,14 @@
+import { Injectable, Logger } from '@nestjs/common';
+
+@Injectable()
+export class TransactionLogger {
+  private readonly logger = new Logger('Transaction');
+
+  log(message: string) {
+    this.logger.log(message);
+  }
+
+  error(message: string, error: any) {
+    this.logger.error(`${message}: ${error.message}`, error.stack);
+  }
+}
diff --git a/middleware/src/transaction/transaction.manager.ts b/middleware/src/transaction/transaction.manager.ts
new file mode 100644
index 0000000..8175ec7
--- /dev/null
+++ b/middleware/src/transaction/transaction.manager.ts
@@ -0,0 +1,36 @@
+import { DataSource, QueryRunner } from 'typeorm';
+
+export class TransactionManager {
+  private queryRunner: QueryRunner;
+
+  constructor(private readonly dataSource: DataSource) {
+    this.queryRunner = this.dataSource.createQueryRunner();
+  }
+
+  async startTransaction(isolation: 'READ COMMITTED' | 'REPEATABLE READ' | 'SERIALIZABLE' = 'READ COMMITTED') {
+    await this.queryRunner.connect();
+    await this.queryRunner.startTransaction(isolation);
+  }
+
+  async commitTransaction() {
+    await this.queryRunner.commitTransaction();
+    await this.queryRunner.release();
+  }
+
+  async rollbackTransaction() {
+    await this.queryRunner.rollbackTransaction();
+    await this.queryRunner.release();
+  }
+
+  async createSavepoint(name: string) {
+    await this.queryRunner.query(`SAVEPOINT ${name}`);
+  }
+
+  async rollbackToSavepoint(name: string) {
+    await this.queryRunner.query(`ROLLBACK TO SAVEPOINT ${name}`);
+  }
+
+  getManager() {
+    return this.queryRunner.manager;
+  }
+}
diff --git a/middleware/src/transaction/transaction.middleware.ts b/middleware/src/transaction/transaction.middleware.ts
new file mode 100644
index 0000000..11bb680
--- /dev/null
+++ b/middleware/src/transaction/transaction.middleware.ts
@@ -0,0 +1,37 @@
+import { Injectable, NestMiddleware } from '@nestjs/common';
+import { Request, Response, NextFunction } from 'express';
+import { DataSource } from 'typeorm';
+import { TransactionManager } from './transaction.manager';
+import { TransactionLogger } from './transaction.logger';
+
+@Injectable()
+export class TransactionMiddleware implements NestMiddleware {
+  constructor(private readonly dataSource: DataSource, private readonly logger: TransactionLogger) {}
+
+  async use(req: Request, res: Response, next: NextFunction) {
+    const manager = new TransactionManager(this.dataSource);
+
+    try {
+      await manager.startTransaction();
+
+      // Attach transaction manager to request for manual control if needed
+      (req as any).transactionManager = manager;
+
+      res.on('finish', async () => {
+        if (res.statusCode >= 200 && res.statusCode < 400) {
+          await manager.commitTransaction();
+          this.logger.log('Transaction committed successfully');
+        } else {
+          await manager.rollbackTransaction();
+          this.logger.log('Transaction rolled back due to error');
+        }
+      });
+
+      next();
+    } catch (error) {
+      await manager.rollbackTransaction();
+      this.logger.error('Transaction failed', error);
+      next(error);
+    }
+  }
+}