NestJS: Initialize certain MongoDB collection as soon as connection is made - node.js

Question

I am very new to NestJs and I would like to build a web app that uses MongoDB.
So what I gonna do is whenever as soon as app is loading mongodb connection should be made and add some logic in callback function.
With Express framework this is the code of logic what I wanna do.
mongoose
.connect(mongoDB, {
user: process.env.MONGODB_USER,
pass: process.env.MONGODB_PASSWORD,
useNewUrlParser: true,
useUnifiedTopology: true,
})
.then(async () => {
//don't show the log when it is test
if (process.env.NODE_ENV !== "test") {
console.log("Connected to %s", mongoDB);
console.log("MongoDB is connected ... \n");
initDB.InitializeDB();
dailyReport.DailyReport();
}
})
.catch((err) => {
console.error("App starting error:", err.message);
process.exit(1);
});
In above code there are two functions.
1st: Logging if DB connection is successful or failed
2nd: When successful I initialize some collections and exit app if failed
I saw NestJs documentation to implement this logic here
import { Module } from '#nestjs/common';
import { MongooseModule } from '#nestjs/mongoose';
#Module({
imports: [MongooseModule.forRoot('mongodb://localhost/nest')],
})
export class AppModule {}
But I am not sure where is the callback function for MongoDB connection.
Can anyone give me answer for this by implementing Express logic using NestJs?

Answer 1

You could do the initialization in the onModuleInit() lifecycle method. Check here for more information: https://docs.nestjs.com/fundamentals/lifecycle-events#lifecycle-events
Code would look like this:
#Module({
imports: [MongooseModule.forRoot('mongodb://localhost/nest')],
})
export class AppModule {
#InjectConnection() private connection: Connection;
onModuleInit() {
// execute logic + access mongoDB via this.connection
}
}