NestJS and TypeORM: Cannot use import statement outside a module

If you’re reading this article, chances are you’ve encountered one of the most frustrating errors in NestJS development: “Cannot use import statement outside a module”. Don’t worry, you’re not alone! This error can be perplexing, especially when working with TypeORM. In this article, we’ll delve into the reasons behind this error and provide a step-by-step guide to resolve it.

What is the error about?

The “Cannot use import statement outside a module” error occurs when the JavaScript interpreter encounters an import statement outside a module. In other words, when you try to import a module or a class outside a JavaScript file that is not considered a module.

Why does this error occur in NestJS and TypeORM?

In NestJS, we often use the `@nestjs/typeorm` package to interact with our database using TypeORM. When setting up TypeORM, we need to create a `typeormConfig` file that exports the database configurations. This file is not a module, and therefore, we can’t use import statements inside it.

However, we might need to import some modules or classes within the `typeormConfig` file, which leads to the “Cannot use import statement outside a module” error.

Resolving the Error

Don’t worry, resolving this error is relatively straightforward. Here are the steps to follow:

Step 1: Create a separate module for typeormConfig

Create a new file, e.g., `typeorm.config.module.ts`, and move the entire `typeormConfig` into it. This file should be a module, and therefore, it can contain import statements.

// typeorm.config.module.ts
import { TypeOrmModuleOptions } from '@nestjs/typeorm';
import { ConfigModule } from '@nestjs/config';

@Module()
export class TypeOrmConfigModule {
  @Config('DATABASE_URL')
  private databaseUrl: string;

  getTypeOrmConfig(): TypeOrmModuleOptions {
    return {
      type: 'postgres',
      url: this.databaseUrl,
      entities: [__dirname + '/../**/*.entity{.ts,.js}'],
      migrations: [__dirname + '/../migrations/*{.ts,.js}'],
      synchronize: true,
    };
  }
}

Step 2: Import the TypeOrmConfigModule in your NestJS module

In your NestJS module, import the `TypeOrmConfigModule` and configure TypeORM using the imported module.

// app.module.ts
import { Module } from '@nestjs/common';
import { TypeOrmConfigModule } from './typeorm.config.module';
import { AppController } from './app.controller';
import { AppService } from './app.service';

@Module({
  imports: [
    TypeOrmConfigModule,
    // other imports
  ],
  controllers: [AppController],
  providers: [AppService],
})
export class AppModule {}

Additional Tips and Tricks

Using Environment Variables with TypeORM

In the example above, we used the `@Config` decorator to inject the `DATABASE_URL` environment variable into the `TypeOrmConfigModule`. This approach allows us to decouple our database configuration from our code.

Using a Separate File for TypeORM Migrations

You can also create a separate file for your TypeORM migrations. This approach allows you to keep your migrations organized and separate from your main application code.

// migrations.ts
import { MigrationInterface, QueryRunner } from 'typeorm';

export class CreateUsersTable1588531251146 implements MigrationInterface {
  public async up(queryRunner: QueryRunner): Promise {
    await queryRunner.query(`
      CREATE TABLE users (
        id SERIAL PRIMARY KEY,
        name VARCHAR(255) NOT NULL,
        email VARCHAR(255) UNIQUE NOT NULL
      );
    `);
  }

  public async down(queryRunner: QueryRunner): Promise {
    await queryRunner.query(`
      DROP TABLE users;
    `);
  }
}

Common Pitfalls

Forgetting to Import the TypeOrmConfigModule

Remember to import the `TypeOrmConfigModule` in your NestJS module. If you forget to do so, TypeORM won’t be configured correctly, and you’ll encounter errors.

Not Defining the TypeOrmConfigModule as a Module

Make sure to define the `TypeOrmConfigModule` as a module using the `@Module` decorator. If you don’t, it won’t be recognized as a module, and you’ll encounter the “Cannot use import statement outside a module” error.

Conclusion

In this article, we’ve explored the “Cannot use import statement outside a module” error in NestJS and TypeORM. We’ve learned how to resolve this error by creating a separate module for our TypeORM configuration and importing it in our NestJS module. Additionally, we’ve covered some best practices and common pitfalls to avoid when working with TypeORM in NestJS.

By following the steps outlined in this article, you should be able to resolve the “Cannot use import statement outside a module” error and configure TypeORM correctly in your NestJS application.

Troubleshooting Checklist
Have you created a separate module for your TypeORM configuration?
Have you imported the TypeOrmConfigModule in your NestJS module?
Have you defined the TypeOrmConfigModule as a module using the @Module decorator?
Have you checked for any typos or syntax errors in your code?

If you’re still encountering issues, feel free to ask in the comments below, and I’ll be happy to help!

Related Articles

• NestJS and TypeORM Tutorial: A Beginner’s Guide
• NestJS and TypeORM Error Handling: Best Practices
• NestJS and TypeORM Performance Optimization: Tips and Tricks

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