How to make a complete/proper GraphQL API with Nest.js?

Creating a complete and proper GraphQL API with Nest.js involves several key steps, from setting up your Nest.js environment to defining schemas, resolvers, and integrating with a database. Here's a detailed guide to help you build a GraphQL API using Nest.js:

1. Setting Up Your Nest.js Project

First, you need to create a new Nest.js project if you haven't already. You can do this by installing the Nest CLI and creating a new project:

npm i -g @nestjs/cli
nest new project-name
cd project-name

2. Install GraphQL and Apollo Server Packages

Nest.js uses Apollo Server under the hood for serving GraphQL APIs. Install the necessary packages:

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

3. Set Up GraphQL Module

Create a GraphQL module using the Nest CLI and configure it in your app:

nest generate module graphql

In your app.module.ts, import the GraphQLModule and configure it:

import { Module } from '@nestjs/common';
import { GraphQLModule } from '@nestjs/graphql';
import { ApolloDriver, ApolloDriverConfig } from '@nestjs/apollo';

@Module({
  imports: [
    GraphQLModule.forRoot<ApolloDriverConfig>({
      driver: ApolloDriver,
      autoSchemaFile: 'schema.gql',  // Generates schema automatically in memory
    }),
  ],
})
export class AppModule {}

4. Define Your GraphQL Schemas

You can define your schemas using either code first or schema first approach. Here’s an example using the code first approach:

Create a recipe.entity.ts:

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

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

  @Field()
  title: string;

  @Field({ nullable: true })
  description?: string;
}

5. Create Resolvers

Resolvers are where you define the methods that will respond to the GraphQL queries. Create a resolver for the Recipe:

nest generate resolver recipe

Implement the resolver in recipe.resolver.ts:

import { Query, Resolver } from '@nestjs/graphql';
import { Recipe } from './entities/recipe.entity';

@Resolver(of => Recipe)
export class RecipeResolver {
  @Query(returns => [Recipe])
  async recipes(): Promise<Recipe[]> {
    return [
      {
        id: '1',
        title: 'First Recipe',
        description: 'Delicious first recipe',
      },
    ];
  }
}

6. Integrate with a Database

To make your API dynamic, integrate it with a database like MongoDB or PostgreSQL. For example, using TypeORM with PostgreSQL:

npm install @nestjs/typeorm typeorm pg

Configure the TypeORM module in your app.module.ts and use repositories in your services to interact with the database.

7. Authentication and Authorization

For securing your GraphQL API, you might want to add authentication and authorization:

Authentication: You can use Passport with JWT or other strategies to authenticate users.
Authorization: You can use Guards to protect specific routes or use field-level authorization with directives.

8. Testing and Documentation

Testing: Write unit and e2e tests using Jest that comes pre-configured with Nest.js.
Documentation: Although GraphQL has built-in documentation through the playground, you may want to maintain a versioned API documentation using tools like Swagger (for REST) or GraphDoc (for GraphQL).

By following these steps, you'll have a robust, scalable, and secure GraphQL API using Nest.js.

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