NestJS Development Company

Leverage Nest’s strong DI to handle dependencies with regards to your modules and services. Services such as controllers or other services can get dependency injected from a provider or simply a service, repository etc.

Use @Module for defining providers and use @Injectable() in order to make classes injectable.

Tip: The @Inject() qualification should be used with tokens when one needs to inject explicit or nonstandard implementations.

Consequently, you need to divide your application into clean different modules. Every of them could encompass certain functionality associated with a particular subject.

That is, AuthModule or DatabaseModule which depends on the problem, are common and can be used in other feature modules.

Tip: If the module is needed in many others, for example, DatabaseModule, make it a global one with @Global() before @Module().

There is a one-time useful custom decorators in controllers such as @CurrentUser() or @Roles().

Middleware is useful for embedding preliminary requests before reaching the controllers (for instance logging, authentication among others).

Tip: @SetMetadata() should be used together with @UseGuards() for role-based access control as well as custom guards.

Through interceptors you can modify the response and perform cross-cutting operations such as logging, caching and exception management.

For instance, MapInterceptor to apply transformations to the API responses, TimeoutInterceptor to set a timeout for an API call.

Tip: In WebSphere sMash, use the ClassSerializerInterceptor to mask values or serialize entities on the response level.

Many exceptions should be handled uniformly throughout the application and this can be achieved by using filters. Nest has @Catch(HttpException) and custom exception filters to catch certain exceptions.

Tip: New an HttpExceptionFilter to take care of all exceptions by inheriting from the existing class and using the app.useGlobalFilters(new YourGlobalExceptionFilter()); in the main.ts file.

Database operations are easier with Nest due to its close integration with both TypeORM and Prisma.

Take advantage of repositories to handle your complicated search cases and ensure your service is clean.

Tip: This is where the QueryBuilder in TypeORM comes into play when building up more complicated queries and be sure to use transactions for operations requiring consistency when spanning several stages.

The configuration management of different environments is made easy by the @nestjs/config module.

Source control configuration files and use a combination of.env files to store legit environment variables.

Tip: It is recommended to use Joi validation with your configuration to validate the environment variables, during startup to avoid any runtime issues.

This is the practice implemented in NestJS, and the unit test framework used here is Jest.

This high level of coupling should be reduced through unit testing of the services and, where possible the use of mock services.

Tip: When writing tests consider using @nestjs/testing to create a testing module in your tests for your controllers and modules that use DI.

Middleware should be used when you have generic pre-processing logic to perform, for instance, logging, verification of the request’s appropriateness or token extraction.

By using NestJS, you are allowed to use middleware locally for a specific module or apply it across the application.

There is also CacheModule which can be used to cache responses or some frequently accessed information.

By doing the caching and lazy loading calls the database queries can be optimized and the frequency of calls can also be minimized.

Tip: The usage of caching interceptors is added by using APP_INTERCEPTOR to apply caching at the application level.

Use @nestjs/passport and passport for authentication and specifically jwt for stateless authentication.

CSRF protection should always be done, and request body size should be limited when implementing the HTTP protocol.

Tip: Lock your configuration, hide information in your response and use helmet for setting security headers.

For all file inputs, you should use FileInterceptor that is provided by @nestjs/platform-express.

For more extensive works that require storage, link it to cloud storage (e.g. S3) or to local storage, if necessary.

Tip: The FileInterceptor can be used with custom storage options to make handling of the file upload paths more flexible. 

These practices should help to create competently and write comprehensible code, which will be easy to maintain in the future NestJS applications. If you want more detailed advice base on your problem such as implementing DI for custom repositories or using particular library, feel free to tell me the detail and I can help you out further.