How to create GraphQL API in Nest JS? Step by Step guidelines!

Creating a GraphQL API in NestJS involves several steps. Here's a step-by-step theoretical guide:

Step 1: Setup a New NestJS Project

Install Nest CLI:

   npm install -g @nestjs/cli

Create a New Project:

   nest new project-name

Navigate to the Project Directory:

   cd project-name

Step 2: Install GraphQL and Apollo Server

Install Required Packages:

   npm install @nestjs/graphql graphql apollo-server-express

Step 3: Configure GraphQL Module

Create a GraphQL Module Configuration: Open src/app.module.ts and configure the GraphQL module:

   import { Module } from '@nestjs/common';
   import { GraphQLModule } from '@nestjs/graphql';
   import { join } from 'path';

   @Module({
     imports: [
       GraphQLModule.forRoot({
         autoSchemaFile: join(process.cwd(), 'src/schema.gql'),
       }),
     ],
   })
   export class AppModule {}

Step 4: Create a Resolver

Generate a Resolver: Use the Nest CLI to generate a resolver:

   nest g resolver user

Define Resolver Logic: Open src/user/user.resolver.ts and define the resolver logic:

   import { Resolver, Query, Mutation, Args } from '@nestjs/graphql';
   import { UserService } from './user.service';
   import { User } from './user.entity';
   import { CreateUserInput } from './dto/create-user.input';

   @Resolver(of => User)
   export class UserResolver {
     constructor(private readonly userService: UserService) {}

     @Query(returns => [User])
     async users() {
       return this.userService.findAll();
     }

     @Mutation(returns => User)
     async createUser(@Args('createUserInput') createUserInput: CreateUserInput) {
       return this.userService.create(createUserInput);
     }
   }

Step 5: Create a Service

Generate a Service: Use the Nest CLI to generate a service:

   nest g service user

Implement Service Logic: Open src/user/user.service.ts and implement the service logic:

   import { Injectable } from '@nestjs/common';
   import { User } from './user.entity';
   import { CreateUserInput } from './dto/create-user.input';

   @Injectable()
   export class UserService {
     private users: User[] = [];

     findAll(): User[] {
       return this.users;
     }

     create(createUserInput: CreateUserInput): User {
       const user = { ...createUserInput, id: Date.now().toString() };
       this.users.push(user);
       return user;
     }
   }

Step 6: Define GraphQL Schema and DTOs

Create GraphQL Schema and DTOs: Create the src/user/user.entity.ts:

   import { ObjectType, Field, ID } from '@nestjs/graphql';

   @ObjectType()
   export class User {
     @Field(type => ID)
     id: string;

     @Field()
     name: string;

     @Field()
     email: string;
   }

Create the src/user/dto/create-user.input.ts:

   import { InputType, Field } from '@nestjs/graphql';

   @InputType()
   export class CreateUserInput {
     @Field()
     name: string;

     @Field()
     email: string;
   }

Step 7: Update Module

Update the Module to include Resolver and Service: Open src/user/user.module.ts and update it:

   import { Module } from '@nestjs/common';
   import { UserService } from './user.service';
   import { UserResolver } from './user.resolver';

   @Module({
     providers: [UserService, UserResolver],
   })
   export class UserModule {}

Step 8: Integrate the User Module

Integrate the User Module into the App Module: Open src/app.module.ts and update it:

   import { Module } from '@nestjs/common';
   import { GraphQLModule } from '@nestjs/graphql';
   import { join } from 'path';
   import { UserModule } from './user/user.module';

   @Module({
     imports: [
       GraphQLModule.forRoot({
         autoSchemaFile: join(process.cwd(), 'src/schema.gql'),
       }),
       UserModule,
     ],
   })
   export class AppModule {}

Step 9: Run the Application

Start the NestJS Application:

   npm run start:dev

Step 10: Test the GraphQL API

Access the GraphQL Playground: Navigate to http://localhost:3000/graphql to access the GraphQL playground and test your API by running queries and mutations.

This guide provides a foundational approach to creating a GraphQL API in NestJS. You can further expand and customize it based on your application's requirements.

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