typescript 37 lines · 7 steps

Wrapping requests in a transaction with NestJS

A NestJS interceptor opens a database transaction per request and commits, rolls back, or releases it based on the handler's outcome.

Explained by highlit
NestJS Advanced interceptors transactions rxjs typeorm request-lifecycle
1import { Injectable, NestInterceptor, ExecutionContext, CallHandler } from '@nestjs/common';
2import { Observable, catchError, concatMap, finalize } from 'rxjs';
3import { DataSource, QueryRunner } from 'typeorm';
4 
5declare module 'express' {
6 interface Request {
7 queryRunner?: QueryRunner;
8 }
9}
10 
11@Injectable()
12export class TransactionInterceptor implements NestInterceptor {
13 constructor(private readonly dataSource: DataSource) {}
14 
15 async intercept(context: ExecutionContext, next: CallHandler): Promise<Observable<unknown>> {
16 const request = context.switchToHttp().getRequest();
17 const queryRunner = this.dataSource.createQueryRunner();
18 
19 await queryRunner.connect();
20 await queryRunner.startTransaction();
21 request.queryRunner = queryRunner;
22 
23 return next.handle().pipe(
24 concatMap(async (data) => {
25 await queryRunner.commitTransaction();
26 return data;
27 }),
28 catchError(async (err) => {
29 await queryRunner.rollbackTransaction();
30 throw err;
31 }),
32 finalize(() => {
33 void queryRunner.release();
34 }),
35 );
36 }
37}
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Interceptors can wrap the entire request lifecycle, running setup before the handler and teardown after its result stream resolves.
  2. 2RxJS operators let you branch cleanup logic on success versus error while guaranteeing a final release regardless of outcome.
  3. 3Attaching a per-request QueryRunner to the request object hands the same transactional connection to downstream handlers.

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