Simple example with NestJS and Mercurius (Schema First) 😻

In this post I will show you how to implement NestJS😻 with GraphQL in schema first mode, using Mercurius and the "platform" to Fastify.

For those unfamiliar with NestJS, it's a Node.js TypeScript framework that helps you build efficient and scalable enterprise-grade Node.js applications.

While for those unfamiliar with GraphQL it is a powerful query language for APIs and a runtime to satisfy those queries with existing data. It's an elegant approach that solves many typical REST API problems.

Mercurius, on the other hand, is a GraphQL adapter for Fastify (for others information see the documentation here).

I attach here the link to see the difference between GraphQL vs REST.

The ways to use GraphQL are two first the code or first the schema, the first from the code we create the schema for GraphQL while the second we create our schema that interfaces with GraphQL.

In this example we are going to see the schema first mode with the use of TypeORM, but you can use whatever you like.

Well now after this short intro let's get started!

So let's get started by creating the NestJS app

Open Terminal and install CLI for NestJS, if you have already installed it, skip this step.

$ npm i -g @nestjs/cli

Then create a NestJS project.

$ nest new nestjs-graphql-mercurius-schema-first
$ cd nestjs-graphql-mercurius-schema-first
// start the application
$ npm run start:dev

Open the browser on localhost:3000 to verify that hello world is displayed.

Well, the first thing to do before installing the dependencies for graphql and mercurius is to install the @nestjs/platform-fastify package instead of the default express-based @nestjs/platform-express package, because mercurius works with Fastify and not with Express, to do so follow these steps:

npm remove @nestjs/platform-express

and install the dependency for Fastify

npm install @nestjs/platform-fastify

We now modify the file main.ts, configuring the adapter for Fastify within the boostrap function, like this:

import { NestFactory } from '@nestjs/core';
import {
  FastifyAdapter,
  NestFastifyApplication,
} from '@nestjs/platform-fastify';
import { AppModule } from './app.module';

async function bootstrap() {
  const app = await NestFactory.create<NestFastifyApplication>(
    AppModule,
    new FastifyAdapter()
  );
  await app.listen(3000);
}
bootstrap();

now we open the browser again on localhost:3000 or via curl (curl -H 'content-type: application/json' -v -X GET http://127.0.0.1:3000) to verify that "hello world" is displayed.

Good! Now let's proceed with configuring the database with docker by creating a docker-compose.yml file to create the PostgreSQL service, things follows:

services:
  db:
    image: postgres
    restart: always
    ports:
      - "5432:5432"
    environment:
      POSTGRES_USER: postgres
      POSTGRES_PASSWORD: pass123
      POSTGRES_DB: postgres

for those who do not know what docker is I leave you the link here for more information: https://www.docker.com/get-started

There are many different ways to integrate Nest with databases, and all of them depend on personal preferences or project needs.

Install graphql dependencies and devDependencies

$ npm i @nestjs/graphql @nestjs/mercurius graphql mercurius

Create a GraphqlOptions class for GraphQL settings, as follows:

import { GqlOptionsFactory } from '@nestjs/graphql';
import { Injectable } from '@nestjs/common';
import { join } from 'path';
import { MercuriusDriverConfig } from '@nestjs/mercurius';

@Injectable()
export class GraphqlOptions implements GqlOptionsFactory {
  createGqlOptions(): Promise<MercuriusDriverConfig> | MercuriusDriverConfig {
    return {
      subscription: true,
      graphiql: true,
      typePaths: ['./**/*.graphql'],
      definitions: {
        path: join('./graphql.schema.ts'),
        outputAs: 'class',
      },
    };
  }
}

An important thing about this configuration is to set where we want the graphql.schema.ts file to be generated, you can call it whatever you want, the important thing is to prefix it with* .ts.

Well now let's move on to registering GraphQLModule in AppModule:

@Module({
    imports:[ 
       GraphQLModule.forRootAsync<MercuriusDriverConfig>({
          driver: MercuriusDriver,
          useClass: GraphqlOptions,
       }),
    ],
})
export class AppModule {}

Now let's create a file called users.graphql, where we are going to write our scheme that allows us to interact later with Graphiql Playground:

type User {
  id: ID
  name: String!
  email: String!
  username: String!
  password: String!
}

input CreateUserInput {
  name: String!
  email: String!
  username: String!
  password: String!
}

input UpdateUserInput {
  name: String!
  email: String!
  username: String!
  password: String!
}

type Query {
  users: [User]!
  user(id: Int!): User
}

type Mutation {
  createUser(createUserInput: CreateUserInput!): User!
  updateUser(id: Int!, updateUserInput: UpdateUserInput!): User!
  removeUser(id: Int!): User
}

In this file we have set up a lot of things before, we have a User object type and two inputs which are like DTO, which in turn allows us to define how the request should look. To complete our users.graphql file we have created two other types called Query and Mutation.
In very simple words, the use of the query in graphql is used to retrieve the data while the mutation is used for operations such as inserting and updating data or to delete data.

Well, now let's move on to installing dependencies for Typeorm.

Install TypeORM and PostgreSQL dependencies

$ npm install --save @nestjs/typeorm typeorm pg

We also install another package for configuration files such as .env files (environments)

$ npm install --save @nestjs/config

Set TypeOrmModule and ConfigModule in AppModule

import { Module } from '@nestjs/common';
import { TypeOrmModule } from '@nestjs/typeorm';

@Module ({
   imports: [
    ConfigModule.forRoot(),
    TypeOrmModule.forRootAsync({
      useFactory: () => ({
        type: 'postgres',
        host: process.env.DATABASE_HOST,
        port: +process.env.DATABASE_PORT,
        username: process.env.DATABASE_USER,
        password: process.env.DATABASE_PASSWORD,
        database: process.env.DATABASE_NAME,
        autoLoadEntities: true,
        synchronize: true,
      }),
    }),
   ],
})
export class AppModule {}

Create a .env file, as follows:

  DATABASE_HOST=localhost
  DATABASE_USER=postgres
  DATABASE_PASSWORD=pass123
  DATABASE_NAME=postgres
  DATABASE_PORT=5432

If you have trouble setting up TypeOrmModule here, make sure Docker is running with docker compose up.
Also make sure the database name inside your .env matches the one you have in your docker-compose file.

Well now let's create our entity we call it users.entity.ts:

import { Column, Entity, PrimaryGeneratedColumn } from 'typeorm';

@Entity()
export class User {
  @PrimaryGeneratedColumn()
  id: number;

  @Column()
  name: string;

  @Column()
  username: string;

  @Column({
    unique: true,
  })
  email: string;

  @Column({ length: 60 })
  password: string;
}

Create Data Transfer Objects (Dto) class to create the user, which we will call CreateUserInput:

import { Field, InputType } from '@nestjs/graphql';
import { MaxLength, IsNotEmpty, IsEmail, IsString } from 'class-validator';

@InputType()
export class CreateUserInput {
  @IsString()
  @MaxLength(30)
  @Field()
  readonly name: string;

  @IsString()
  @MaxLength(40)
  @Field()
  readonly username: string;

  @IsEmail()
  @Field()
  readonly email: string;

  @IsNotEmpty()
  @IsString()
  @MaxLength(60)
  @Field()
  password: string;
}

Remember to install this package before creating the dto class for the upgrade.

$ npm i @nestjs/mapped-types

Well, now to update the user data we extend the CreateUserInput class:

import { InputType, PartialType } from '@nestjs/graphql';
import { CreateUserInput } from './create-user.input';

@InputType()
export class UpdateUserInput extends PartialType(CreateUserInput) {}

we call validation pipe in the main.ts file as follows:

import { ValidationPipe } from '@nestjs/common';
import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  app.useGlobalPipes(
    new ValidationPipe({
      whitelist: true,
      transform: true,
      forbidNonWhitelisted: true,
      transformOptions: {
        enableImplicitConversion: true,
      },
    }),
  );
  await app.listen(3000);
}
bootstrap();

Well, now we're going to create a simple service, resolver, and user module

$ nest g module users
$ nest g service users
$ nest g resolver users

You should now have a users folder with UsersModule, UsersService, and UsersResolver inside.

Now before we write our service, let's create a final dto file for the pagination, as follows:

import { ArgsType, Field, Int } from '@nestjs/graphql';
import { Max, Min } from 'class-validator';

@ArgsType()
export class UsersArgs {
  @Field(() => Int)
  @Min(0)
  offset = 0;

  @Field(() => Int)
  @Min(1)
  @Max(50)
  limit = 25;
}

Now let's start writing our UsersService:

import { Injectable } from '@nestjs/common';
import { InjectRepository } from '@nestjs/typeorm';
import * as bcrypt from 'bcrypt';
import { Repository } from 'typeorm';
import { CreateUserInput } from './dto/create-user.input';
import { UpdateUserInput } from './dto/update-user.input';
import { UsersArgs } from './dto/users.args';
import { Users } from './entities/users.entity';
import { ErrorWithProps } from 'mercurius';

@Injectable()
export class UsersService {
  constructor(
    @InjectRepository(Users)
    private readonly usersRepository: Repository<Users>,
  ) {}

  public async findAll(usersArgs: UsersArgs): Promise<Users[]> 
  {
    const { limit, offset } = usersArgs;
    return this.usersRepository.find({
      skip: offset,
      take: limit,
    });
  }

  public async findOneById(id: string): Promise<Users> {
    const user = await this.usersRepository.findOne(id);

    if (!user) {
      throw new ErrorWithProps(`User #${id} not found`);
    }
    return user;
  }

  public async create(createUserInput: CreateUserInput): Promise<Users> {
    createUserInput.password = bcrypt.hashSync(createUserInput.password, 8);

    const user = this.usersRepository.create({ ...createUserInput});
    return this.usersRepository.save(user);
  }

  public async update(
    id: string,
    updateUserInput: UpdateUserInput,
  ): Promise<Users> {
    updateUserInput.password = bcrypt.hashSync(updateUserInput.password, 8);

    const user = await this.usersRepository.preload({
      id: +id,
      ...updateUserInput,
    });

    if (!user) {
      throw new ErrorWithProps(`User #${id} not found`);
    }
    return this.usersRepository.save(user);
  }

  public async remove(id: string): Promise<any> {
    const user = await this.findOneById(id);
    return this.usersRepository.remove(user);
  }
}

UserResolver:

import { NotFoundException } from '@nestjs/common';
import { Args, Mutation, Query, Resolver } from '@nestjs/graphql';
import { CreateUserInput, UpdateUserInput, UsersArgs } from './dto';
import { UsersService } from './users.service';
import { Users } from './entities/users.entity';
import { ErrorWithProps } from 'mercurius';

@Resolver()
export class UsersResolver {
  constructor(private readonly usersService: UsersService) {}

  @Query(() => [Users])
  public async users(@Args() usersArgs: UsersArgs): Promise<Users[]> {
    return this.usersService.findAll(usersArgs);
  }

  @Query(() => Users)
  public async user(@Args('id') id: string): Promise<Users> {
    const user = await this.usersService.findOneById(id);
    if (!user) {
      throw new ErrorWithProps(`User #${id} not found`);
    }
    return user;
  }

  @Mutation(() => Users)
  public async createUser(
    @Args('createUserInput') createUserInput: CreateUserInput,
  ): Promise<Users> {
    return await this.usersService.create(createUserInput);
  }

  @Mutation(() => Users)
  public async updateUser(
    @Args('id') id: string,
    @Args('updateUserInput') updateUserInput: UpdateUserInput,
  ): Promise<Users> {
    return await this.usersService.update(id, updateUserInput);
  }

  @Mutation(() => Users)
  public async removeUser(@Args('id') id: string): Promise<any> {
    return this.usersService.remove(id);
  }
}

Now register in our UsersModule our service and the resolver, like this:

import { Module } from '@nestjs/common';
import { TypeOrmModule } from '@nestjs/typeorm';
import { UsersService } from './users.service';
import { UsersResolver } from './users.resolver';
import { Users } from './entities/users.entity';

@Module({
  imports: [TypeOrmModule.forFeature([Users])],
  providers: [UsersService, UsersResolver],
})
export class UsersModule {}

Well now let's try to interact with GraphQL to see if everything works, but before we have to verify that starting our application the schema.gql file is generated, once done, from the browser we go to the address http://localhost:3000/graphiql thus starting our GraphiQL ( the Graphiql Playground for Mercurius), a UI that allows us to interact with our database.

I add below the Queries and Mutations to run in the Graphiql:

getUsers

{
    users {
        id
        name
        email
        username
        password
    }
}

getUserById

{
    user(id: "1") {
        id
        name
        email
        username
        password
    }
}

addUser

mutation {
    createUser(createUserInput: {
        name: "tony"
        email:"[e-mail]"
        username: "tony_admin"
        password: "secret123"
    }) {
        name
        email
        username
        password
    }
}

updateUser

mutation {
    updateUser(
        updateUserInput: {
            name: "tony"
            email: "[e-mail]"
            username: "tony_admin"
            password: "secret123"
        }
        id: "1"
    ) {
        name
        email
        username
        password
    }
}

removeUser

mutation {
    removeUser(id: "3") {
        name
        email
        username
        password
    }
}

That's all.

I hope it will be helpful for anything write me in the comments as well.😉