How can you implement a task scheduler in Nest.js?

Implementing a task scheduler in Nest.js can be done in two primary approaches: using the built-in @nestjs/schedule module or third-party libraries such as node-cron. Below is a detailed explanation and examples for both methods.

Using the @nestjs/schedule Module

Nest.js officially provides a task scheduling module @nestjs/schedule, which implements scheduled tasks using cron and setTimeout/setInterval. This module offers high integration with the Nest.js framework and is user-friendly.

Step 1: Install the Module

First, install the @nestjs/schedule module and cron using npm or yarn:

bash
npm install --save @nestjs/schedule
npm install --save cron

Step 2: Import ScheduleModule

Import ScheduleModule into your application module (typically AppModule):

typescript
import { Module } from '@nestjs/common';
import { ScheduleModule } from '@nestjs/schedule';
import { TasksService } from './tasks.service';

@Module({
  imports: [
    ScheduleModule.forRoot()
  ],
  providers: [TasksService],
})
export class AppModule {}

Step 3: Create a Task Service

Next, create a service to define your scheduled tasks:

typescript
import { Injectable } from '@nestjs/common';
import { Cron, CronExpression } from '@nestjs/schedule';

@Injectable()
export class TasksService {
  @Cron(CronExpression.EVERY_HOUR)
  handleCron() {
    // This function executes every hour
    console.log('Run this task every hour');
  }
}

In the above code, we use the @Cron decorator to define a task that runs hourly. CronExpression is a predefined enumeration providing common cron configurations.

Using the node-cron Library

For greater flexibility, node-cron is a popular third-party library offering extensive cron task configuration options.

Step 1: Install node-cron

Install node-cron using npm or yarn:

bash
npm install --save node-cron

Step 2: Create Scheduled Tasks

Use node-cron to set up tasks within a service:

typescript
import { Injectable } from '@nestjs/common';
import * as cron from 'node-cron';

@Injectable()
export class CronJobsService {
  constructor() {
    this.scheduleTasks();
  }

  private scheduleTasks() {
    cron.schedule('0 * * * *', () => {
      console.log('Run this task every hour');
    }, {
      scheduled: true,
      timezone: "Asia/Shanghai"
    });
  }
}

In this example, we use cron.schedule to set up a task executing hourly. You can freely configure execution times using cron expressions.

Summary

The above are the two primary methods for implementing task scheduling in Nest.js. The choice depends on your project requirements and preferences regarding integration depth and third-party dependencies. @nestjs/schedule provides tighter integration with Nest.js, while node-cron offers greater flexibility and features.