Nestjs : How to use mongoose to start a session for transaction?

1. Install and Configure the Mongoose Module: First, install the required packages: @nestjs/mongoose and mongoose. This can be accomplished by executing the following command:

   bash
   npm install @nestjs/mongoose mongoose

   Next, import MongooseModule into your NestJS module using .forRoot() or .forRootAsync() to establish a connection to the MongoDB database.

2. Create a Schema: Define a Mongoose schema to enable NestJS to interact with specific MongoDB collections.

3. Inject the Model into the Service: In your service file, inject the corresponding model via the constructor.

4. Start the Transaction Session: In the service, access the database connection using the db property of the injected model and start a new transaction session with startSession(). Then, use this session to execute transactional operations.

Here is a simplified example demonstrating how to start and use a Mongoose transaction in a NestJS service:

typescript
import { Injectable } from '@nestjs/common';
import { InjectModel } from '@nestjs/mongoose';
import { Model } from 'mongoose';
import { YourDocument, YourSchema } from './schemas/your.schema';

@Injectable()
export class YourService {
  constructor(@InjectModel(YourSchema.name) private yourModel: Model<YourDocument>) {}

  async doSomethingInTransaction(): Promise<any> {
    // Create a new session
    const session = await this.yourModel.db.startSession();
    // Start the transaction
    session.startTransaction();
    try {
      // Here, perform operations using the transaction session, such as:
      // const result = await this.yourModel.create([{ ... }], { session: session });
      // await anotherModel.updateOne({ _id: id }, { $set: { ... } }, { session: session });
      // ...

      // If all operations succeed, commit the transaction
      await session.commitTransaction();
    } catch (error) {
      // If any operation fails, abort all changes
      await session.abortTransaction();
      // Re-throw the error or handle it
      throw error;
    } finally {
      // End the session
      session.endSession();
    }
  }
}

This is the basic workflow for implementing transaction operations with Mongoose in NestJS. In actual applications, you must implement database operations based on your specific business logic and handle more complex error scenarios.