Building a GraphQL API with Nest.js and Apollo

In this article, we'll explore how to build a GraphQL API using Nest.js and Apollo. We'll cover the basics of GraphQL, how to set up a new Nest.js project, and how to use Apollo to create a GraphQL API. By the end of this article, you'll have a fully functional GraphQL API that you can use as a starting point for your own projects.

What is GraphQL?

GraphQL is a query language for APIs that allows clients to specify exactly what data they need, and receive only that data in response. This approach is different from traditional REST APIs, where clients typically receive a fixed set of data in response to a request.

GraphQL has several benefits, including:

• Improved performance: By only receiving the data that's needed, clients can reduce the amount of data that's transferred over the network.
• Increased flexibility: GraphQL allows clients to specify exactly what data they need, which makes it easier to add new features or modify existing ones.
• Reduced overhead: GraphQL eliminates the need for multiple requests to retrieve related data, which reduces the overhead of making multiple requests.

Setting up a new Nest.js project

To get started with building a GraphQL API using Nest.js and Apollo, we'll need to set up a new Nest.js project. We can do this using the Nest.js CLI:

npm i -g @nestjs/cli
nest new graphql-api

This will create a new Nest.js project called `graphql-api`. We can then navigate into the project directory and install the required dependencies:

cd graphql-api
npm install

Installing Apollo

To use Apollo with Nest.js, we'll need to install the `@nestjs/graphql` package:

npm install @nestjs/graphql

This package provides a set of decorators and classes that we can use to define our GraphQL schema.

Defining the GraphQL schema

To define our GraphQL schema, we'll create a new file called `schema.graphql` in the `src` directory:

type Query {
  hello: String!
}

type Mutation {
  createPost(title: String!, content: String!): Post
}

type Post {
  id: ID!
  title: String!
  content: String!
}

This schema defines three types: `Query`, `Mutation`, and `Post`. The `Query` type has a single field called `hello` that returns a string. The `Mutation` type has a single field called `createPost` that takes two arguments (`title` and `content`) and returns a `Post` object. The `Post` type has three fields: `id`, `title`, and `content`.

Implementing the resolvers

To implement the resolvers for our GraphQL schema, we'll create a new file called `resolvers.ts` in the `src` directory:

import { Resolver, Query, Mutation, Args } from '@nestjs/graphql';

@Resolver()
export class AppResolver {
  @Query(() => String)
  hello(): string {
    return 'Hello World!';
  }

  @Mutation(() => Post)
  createPost(@Args('title') title: string, @Args('content') content: string): Post {
    const post = new Post();
    post.title = title;
    post.content = content;
    return post;
  }
}

class Post {
  id: string;
  title: string;
  content: string;
}

This code defines two resolvers: one for the `hello` query and one for the `createPost` mutation. The `hello` resolver simply returns the string "Hello World!". The `createPost` resolver creates a new `Post` object and returns it.

Creating the GraphQL module

To create the GraphQL module, we'll create a new file called `graphql.module.ts` in the `src` directory:

import { Module } from '@nestjs/common';
import { GraphQLModule } from '@nestjs/graphql';
import { AppResolver } from './resolvers';

@Module({
  imports: [
    GraphQLModule.forRoot({
      autoSchemaFile: 'schema.graphql',
    }),
  ],
  providers: [AppResolver],
})
export class GraphQLModule {}

This code defines the GraphQL module and imports the `AppResolver` class. It also configures the GraphQL module to use the `schema.graphql` file as the schema file.

Starting the application

To start the application, we can use the following command:

npm run start

This will start the application and make the GraphQL API available at `http://localhost:3000/graphql`.

Testing the API

To test the API, we can use a tool like GraphQL Playground. We can access GraphQL Playground by navigating to `http://localhost:3000/graphql` in our web browser.

Once we're in GraphQL Playground, we can test the API by running queries and mutations. For example, we can run the following query to retrieve the `hello` field:

query {
  hello
}

This should return the string "Hello World!". We can also run the following mutation to create a new post:

mutation {
  createPost(title: "My Post", content: "This is my post") {
    id
    title
    content
  }
}

This should create a new post and return the post's `id`, `title`, and `content` fields.

Conclusion

In this article, we've learned how to build a GraphQL API using Nest.js and Apollo. We've covered the basics of GraphQL, how to set up a new Nest.js project, and how to use Apollo to create a GraphQL API. We've also implemented resolvers for our GraphQL schema and created a GraphQL module. Finally, we've tested the API using GraphQL Playground.

Frequently Asked Questions

What is GraphQL?

GraphQL is a query language for APIs that allows clients to specify exactly what data they need, and receive only that data in response.

What is Nest.js?

Nest.js is a framework for building server-side applications in Node.js.

What is Apollo?

Apollo is a set of tools for building GraphQL APIs.

How do I install Apollo?

You can install Apollo using the following command: `npm install @nestjs/graphql`

How do I define a GraphQL schema?

You can define a GraphQL schema using the `type` keyword. For example: `type Query { hello: String! }`

How do I implement resolvers?

You can implement resolvers using the `@Resolver` decorator. For example: `@Resolver() export class AppResolver { ... }`

How do I create a GraphQL module?

You can create a GraphQL module using the `@Module` decorator. For example: `@Module({ imports: [GraphQLModule.forRoot({ autoSchemaFile: 'schema.graphql' })] })`