Introduction

Apollo Server is a popular choice for implementing GraphQL servers, including within NestJS applications. However, several alternatives offer different features, performance characteristics, and benefits. This document explores some of these alternatives, focusing on Mercurius and comparing them to Apollo Server in a NestJS context.

Alternatives to Apollo Server

Besides Mercurius, here are some alternatives for building GraphQL servers:

• GraphQL Yoga: A fully-featured, production-ready GraphQL Server with focus on easy setup and developer experience. Great for getting started quickly.
• Envelop: A flexible GraphQL middleware that can be used with various server implementations. Offers a plugin-based architecture for adding features like tracing, validation, and caching.
• Fastify GraphQL: A plugin for Fastify (a fast and low overhead web framework) that allows you to create GraphQL endpoints.
• GraphQL Helix: A set of utilities for building GraphQL endpoints. Provides a more low-level approach, giving you more control over the request handling.

Exploring Mercurius in NestJS

Mercurius is a GraphQL adapter for Fastify, a performant and lightweight web framework. It boasts excellent performance and offers seamless integration with Fastify's ecosystem. This makes it a compelling alternative to Apollo Server, especially when performance is a critical concern.

Key Features and Benefits of Mercurius:

• Performance: Built on top of Fastify, Mercurius is known for its high performance and low overhead.
• Easy Integration with Fastify: Seamlessly integrates with Fastify's ecosystem, including plugins for logging, validation, and authentication.
• Subscriptions: Supports GraphQL subscriptions for real-time data updates.
• Federation: Supports GraphQL federation, allowing you to build a single, unified GraphQL API from multiple services.
• Simple Configuration: Offers a relatively straightforward configuration process.

Mercurius Example in NestJS

To use Mercurius in a NestJS application, you would typically use a Fastify adapter. Here's a simplified example:

 // app.module.ts
import { Module } from '@nestjs/common';
import { GraphQLModule } from '@nestjs/graphql';
import { MercuriusDriver, MercuriusDriverConfig } from '@nestjs/mercurius';
import { AppController } from './app.controller';
import { AppService } from './app.service';
import { RecipesModule } from './recipes/recipes.module';

@Module({
  imports: [
    GraphQLModule.forRoot({
      driver: MercuriusDriver,
      autoSchemaFile: 'schema.gql', // Or use buildSchema option
      graphiql: true, // Enable GraphiQL interface
    }),
    RecipesModule,
  ],
  controllers: [AppController],
  providers: [AppService],
})
export class AppModule {} 

And a resolver example:

 // recipes/recipes.resolver.ts
import { Query, Resolver } from '@nestjs/graphql';

@Resolver()
export class RecipesResolver {
  @Query(() => String)
  getHello(): string {
    return 'Hello from Mercurius GraphQL!';
  }
} 

You'll also need to install the necessary packages:

 npm install @nestjs/mercurius mercurius graphql 

Comparison: Mercurius vs. Apollo Server in NestJS

When to choose Mercurius:

• When performance is a top priority.
• If you're already using Fastify in your NestJS application or are considering it.
• If you prefer a simpler configuration.

When to choose Apollo Server:

• When you need a very mature and well-supported GraphQL server.
• If you are heavily invested in the Apollo ecosystem (e.g., Apollo Federation, Apollo Client).
• If you require specific Apollo Server features or integrations.

Conclusion

Both Apollo Server and Mercurius are excellent choices for building GraphQL servers in NestJS. The best option depends on your specific needs and priorities. Mercurius offers compelling performance advantages and simpler configuration, while Apollo Server provides a mature and feature-rich ecosystem. By carefully considering your requirements and evaluating the trade-offs, you can choose the right tool for your project.