Service creation in NestJS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a service in NestJS?

A service in NestJS is a class that handles business logic and data management. It is used to keep controllers simple and focused on handling requests.

beginner

How do you create a service using the NestJS CLI?

You run the command <code>nest generate service service-name</code> or <code>nest g s service-name</code>. This creates a service file with a class decorated by <code>@Injectable()</code>.

beginner

What does the @Injectable() decorator do in a NestJS service?

The <code>@Injectable()</code> decorator marks the class as a provider that can be injected into other classes, enabling dependency injection.

intermediate

Why should business logic be placed in services instead of controllers?

Placing business logic in services keeps controllers clean and focused on handling HTTP requests and responses. It also makes the logic reusable and easier to test.

beginner

How do you inject a service into a controller in NestJS?

You inject a service by adding it as a parameter in the controller's constructor. NestJS automatically provides the instance if the service is registered in the module.

Which decorator is used to mark a class as a service provider in NestJS?

A @Injectable()

B @Controller()

C @Service()

D @Module()

The @Injectable() decorator marks a class as a provider that can be injected into other classes.

What command creates a new service using the NestJS CLI?

A nest new service service-name

B nest create service service-name

C nest generate service service-name

D nest build service service-name

The command 'nest generate service service-name' creates a new service file with the proper structure.

Where should you put business logic in a NestJS application?

A In controllers

B In services

C In modules

D In main.ts

Business logic belongs in services to keep controllers simple and reusable.

How do you make a service available to a controller?

A Inject it via the controller's constructor

B Call it directly without injection

C Import it in the controller file

D Declare it in main.ts

Services are injected into controllers through the constructor for dependency injection.

What is the main benefit of using services in NestJS?

A Automatically creates routes

B Makes the app slower

C Removes the need for controllers

D Separates business logic from request handling

Services separate business logic from controllers, improving code organization and testability.

Explain how to create and use a service in NestJS from scratch.

Think about the steps from creating the service file to using it in a controller.

Why is dependency injection important when working with services in NestJS?

Consider how services are provided to other parts of the app.