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https://github.com/Davide-Gheri/nestjs-mercurius

NestJs module to use Mercurius as GraphQL server
https://github.com/Davide-Gheri/nestjs-mercurius

fastify graphql mercurius nestjs

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NestJs module to use Mercurius as GraphQL server

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README 

        


If you want to use Mercurius with @nestjs/graphql > v10, please use the @nestjs/mercurius package





# Nestjs Mercurius



Use [Mercurius GraphQL](https://github.com/mercurius-js/mercurius) with Nestjs framework



Visit the [Wiki](https://github.com/Davide-Gheri/nestjs-mercurius/wiki)



## Install



```bash

npm i @nestjs/platform-fastify fastify mercurius nestjs-mercurius

```



## Use



### Register the module

```typescript

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

import { MercuriusModule } from 'nestjs-mercurius';



@Module({

  imports: [

    // Work also with async configuration (MercuriusModule.forRootAsync)

    MercuriusModule.forRoot({

      autoSchemaFile: true,

      context: (request, reply) => ({

        user: request.user,

      }),

      subscription: {

        context: (connection, request) => ({

          user: request.user,

        }),

      },

    }),

  ],

  providers: [

    CatResolver,

  ],

})

export class AppModule {}

```



### The Object type



```typescript

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



@ObjectType()

export class Cat {

  @Field(() => ID)

  id: number;

  

  @Field()

  name: string;

  

  @Field(() => Int)

  ownerId: number;

}

```



### The Resolver



```typescript

import { Resolver, Query, ResolveField, Parent, Mutation, Subscription, Context, Args } from '@nestjs/graphql';

import { ParseIntPipe } from '@nestjs/common';

import { ResolveLoader, toAsyncIterator, LoaderQuery } from 'nestjs-mercurius';

import { PubSub } from 'mercurius';

import { Cat } from './cat';



@Resolver(() => Cat)

export class CatResolver {

  constructor(

    private readonly catService: CatService,

    private readonly userService: UserService,

  ) {}



  @Query(() => [Cat])

  cats(@Args({name: 'filter', type: () => String, nullable: true}) filter?: string) {

    return this.catService.find(filter);

  }



  @Query(() => Cat, { nullable: true })

  cat(@Args('id', ParseIntPipe) id: number) {

    return this.catService.findOne(id);

  }



  @Mutation(() => Cat)

  createCat(

    @Args('name') name: string,

    @Context('pubsub') pubSub: PubSub,

    @Context('user') user: User,

  ) {

    const cat = new Cat();

    cat.name = name;

    cat.ownerId = user.id;

    //...

    pubSub.publish({

      topic: 'CatCreated',

      payload: { cat },

    });

    return cat;

  }

  

  @Subscription(() => Cat, {

    resolve: (payload) => payload.cat,

    filter: (payload, vars, context) =>

      payload.cat.ownerId !== context.user.id,

  })

  onCatCreated(

    @Context('pubsub') pubSub: PubSub,

  ) {

    return toAsyncIterator(pubSub.subscribe('CatCreated'));

  }

  

  @ResolveField(() => Int)

  age(@Parent() cat: Cat) {

    return 5;

  }

  

  @ResolveLoader(() => User, { opts: { cache: false } })

  owner(

    @Parent() queries: LoaderQuery[],

  ) {

    return this.userService.findById(

      // queries is an array of objects defined as { obj, params } where obj is the current object and params are the GraphQL params

      queries.map(({ obj }) => obj.ownerId)

    );

  }

}

```



## Federation



Install necessary dependencies

```typescript

npm i @apollo/federation

```



### The Gateway



```typescript

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

import { MercuriusGatewayModule } from 'nestjs-mercurius';



@Module({

  imports: [

    MercuriusGatewayModule.forRoot({

      graphiql: 'playground',

      subscription: true,

      gateway: {

        pollingInterval: 10000,

        services: [

          {

            name: 'users',

            url: 'https://....',

            wsUrl: 'wss://...',

          },

          {

            name: 'pets',

            url: 'https://...',

            rewriteHeaders: headers => headers,

          },

        ],

      },

    }),

  ],

})

export class GatewayModule {}

```



### The Service



```typescript

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

import { MercuriusModule } from './mercurius.module';

import { User } from './user';

import { PetResolver, UserResolver } from './resolvers';



@Module({

  imports: [

    MercuriusModule.forRoot({

      autoSchemaFile: true,

      federationMetadata: true,

      buildSchemaOptions: {

        orphanedTypes: [User],

      },

      //...

    }),

  ],

  providers: [

    PetResolver,

    UserResolver,

  ],

})

export class PetModule {}

```



### The Resolver



```typescript

import { Resolver, ResolveReference } from '@nestjs/graphql';

import { Pet } from './pet';

import { Reference } from './reference.interface';



@Resolver(() => Pet)

export class PetResolver {

  constructor(

    private readonly petService: PetService,

  ) {}



  @ResolveReference()

  resolveReference(ref: Reference<'Pet', 'id'>) {

    return this.petService.findOne(ref.id);

  }

}

```



Resolve reference could also be defined as Loader, potentially improving performance:



```typescript

import { ResolveReferenceLoader } from './resolve-reference-loader.decorator';

import { LoaderQuery } from './loader.interface';



@Resolver(() => Pet)

export class PetResolver {

  constructor(

    private readonly petService: PetService,

  ) {}



  @ResolveReferenceLoader()

  resolveReference(refs: LoaderQuery>) {

    return this.petService.findById(

      refs.map(({ obj }) => obj.id)

    );

  }

}

```



## Hooks



Register mercurius hooks as service methods, using the `@GraphQLHook()` decorator



```typescript

import { GraphQLHook } from 'nestjs-mercurius';



@Injectable()

export class HookService {

  @GraphQLHook('preValidation')

  async onPreValidation(schema: GraphQLSchema, source: DocumentNode, context: any) {

   //...

  }

}

```