How do you handle database transactions in Nest.js applications?

Handling database transactions in Nest.js can vary depending on the library used, but the core principle is to ensure that all related database operations either succeed or fail together, maintaining data consistency and integrity. Using TypeORM, the most widely adopted ORM for Nest.js applications, I will provide a detailed explanation of how to handle database transactions.

Handling Transactions with TypeORM

TypeORM is a widely used ORM tool that integrates seamlessly with Nest.js, supporting both Active Record and Data Mapper patterns. When handling transactions, it typically employs the following methods:

1. Using QueryRunner

QueryRunner is a lower-level interface provided by TypeORM for manually controlling database connections, transaction initiation, and termination. Here are the steps to handle transactions using QueryRunner:

1. Obtain Database Connection: First, retrieve a QueryRunner from the data source and use it to manage the database connection.

typescript
const queryRunner = dataSource.createQueryRunner();
await queryRunner.connect();

1. Start Transaction: Begin a new transaction using QueryRunner.

typescript
await queryRunner.startTransaction();

1. Execute Database Operations: Perform all database operations within the transaction. If any operation fails, catch the exception and roll back the transaction.

typescript
try {
    await queryRunner.manager.save(entity1);
    await queryRunner.manager.save(entity2);
    // Additional database operations

    // Commit transaction
    await queryRunner.commitTransaction();
} catch (error) {
    // If an error occurs, roll back the transaction
    await queryRunner.rollbackTransaction();
    throw error;
} finally {
    // Release the database connection held by QueryRunner
    await queryRunner.release();
}

2. Using Transaction Decorators

TypeORM provides the @Transaction() and @TransactionManager() decorators for automatically handling transaction initiation and termination. This approach is more concise than directly using QueryRunner.

typescript
import { Transaction, TransactionManager, EntityManager } from 'typeorm';

class MyService {
    @Transaction()
    async createMultipleEntities(entityDto1, entityDto2, @TransactionManager() manager: EntityManager) {
        await manager.save(Entity1, entityDto1);
        await manager.save(Entity2, entityDto2);
        // Additional operations
    }
}

In this case, TypeORM automatically creates a new transaction for each method decorated with @Transaction(), committing or rolling back the transaction when the method execution completes.

Conclusion

Handling database transactions in Nest.js is recommended to use TypeORM's tools and decorators, as they effectively simplify the complexity of transaction management. Whether manually controlling transactions or leveraging decorators for automatic management, it is crucial to ensure all related operations are processed within the same transaction to maintain data consistency and stability. During development, attention should also be paid to error handling and rollback strategies to prevent data corruption.