Скачать или смотреть How to Use Mongoose with NestJS for Transaction Management

Discover the right approach to handle transactions in NestJS using Mongoose and effectively resolve common connection errors.
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Mastering Transactions in NestJS with Mongoose

When working with databases in any application, handling transactions properly is crucial for consistency and reliability. In the context of using NestJS with Mongoose, developers often encounter issues, especially when starting a session for transactions. One such common issue reported is the error: "Connection 0 was disconnected when calling startSession."

The Problem Explained

The error arises due to a lack of a properly initialized Mongoose connection when trying to start a session. This specific situation can be frustrating, especially when you believe that you've followed the documentation to the letter. You may find yourself in a situation where you have code that looks correct, but you're still running into an endpoint that crashes and throws this connection error.

Here's a look at the original code that leads to this issue:

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Why Does This Error Happen?

For this code to run successfully, Mongoose needs to have an active connection. In the setup with NestJS, using mongoose directly without an active instance results in errors related to disconnecting sessions.

The Solution

After analyzing the NestJS ecosystem along with the Mongoose documentation, the solution revolves around making sure Mongoose is correctly configured within NestJS. Here’s how you can resolve the connection issue:

Step 1: Import Necessary Modules

You will need to import InjectConnection from the @ nestjs/mongoose package, as well as the main mongoose module. Update your imports accordingly:

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Step 2: Update Your Service Constructor

In your service class where you wish to handle transactions, make sure to inject the Mongoose connection using the @ InjectConnection() decorator:

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Step 3: Start Session the Right Way

Replace your original session start line from the direct call to mongoose.startSession() to use the injected connection object:

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Conclusion

By ensuring that you are working with a correctly injected mongoose.Connection instance, you can avoid the disconnection issues when starting sessions for transactions. This approach not only resolves the specific error but also fosters a more reliable and maintainable code structure within your NestJS applications.

With these practical adjustments, you'll be able to effectively manage transactions using Mongoose in a NestJS environment without running into common pitfalls. Happy coding!