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mercurius

API

Plugin options

mercurius supports the following options:

  • schema: String, String[] or schema definition. The graphql schema. The string will be parsed.

  • resolvers: Object. The graphql resolvers.

  • loaders: Object. See defineLoaders for more details.

  • schemaTransforms: Array of schema-transformation functions. Accept a schema as an argument and return a schema.

  • graphiql: boolean | string | Object. Serve GraphiQL on /graphiql if true or 'graphiql'. Leave empty or false to disable. only applies if onlyPersisted option is not true

    An object can be passed in the config to allow the injection of external graphiql plugins exported in umd format.

    • enabled: boolean, default true. Enable disable the graphiql extension
    • plugins: Array
      • name: string. The name of the plugin, it should be the same exported in the umd
      • props: Object | undefined. The props to be passed to the plugin
      • umdUrl: string. The urls of the plugin, it's downloaded at runtime. (eg. https://unpkg.com/myplugin/....)
      • fetcherWrapper: string. A function name exported by the plugin to read/enrich the fetch response

    Check the example folder for detailed usage or this document for a detailed explanation on how to build a plugin.

    Note: If routes is false, this option does not have effects.

  • jit: Integer. The minimum number of execution a query needs to be executed before being jit'ed.

    • Default: 0, jit is disabled.

  • routes: boolean. Serves the Default: true. A graphql endpoint is exposed at /graphql.

  • path: string. Change default graphql /graphql route to another one.

  • context: Function. Result of function is passed to resolvers as a custom GraphQL context. The function receives the request and reply as parameters. It is only called when routes options is true

  • prefix: String. Change the route prefix of the graphql endpoint if enabled.

  • defineMutation: Boolean. Add the empty Mutation definition if schema is not defined (Default: false).

  • errorHandler: Function  or boolean. Change the default error handler (Default: true). Note: If a custom error handler is defined, it should return the standardized response format according to GraphQL spec.

  • errorFormatter: Function. Change the default error formatter. Allows the status code of the response to be set, and a GraphQL response for the error to be defined. This can be used to format errors for batched queries, which return a successful response overall but individual errors, or to obfuscate or format internal errors. The first argument is the ExecutionResult object, while the second one is the context object.

  • queryDepth: Integer. The maximum depth allowed for a single query. Note: GraphiQL IDE sends an introspection query when it starts up. This query has a depth of 7 so when the queryDepth value is smaller than 7 this query will fail with a Bad Request error

  • validationRules: Function or Function[]. Optional additional validation rules that the queries must satisfy in addition to those defined by the GraphQL specification. When using Function, arguments include additional data from graphql request and the return value must be validation rules Function[].

  • subscription: Boolean | Object. Enable subscriptions. It uses mqemitter when it is true and exposes the pubsub interface to app.graphql.pubsub. To use a custom emitter set the value to an object containing the emitter.

    • subscription.emitter: Custom emitter.
    • subscription.pubsub: Custom pubsub, see Subscriptions with custom PubSub for more details. Note that when passing both emitter and pubsub options, emitter will be ignored.
    • subscription.verifyClient: Function A function which can be used to validate incoming connections.
    • subscription.context: Function Result of function is passed to subscription resolvers as a custom GraphQL context. The function receives the connection and request as parameters.
    • subscription.onConnect: Function A function which can be used to validate the connection_init payload. If defined it should return a truthy value to authorize the connection. If it returns an object the subscription context will be extended with the returned object.
    • subscription.onDisconnect: Function A function which is called with the subscription context of the connection after the connection gets disconnected.
    • subscription.keepAlive: Integer Optional interval in ms to send the GQL_CONNECTION_KEEP_ALIVE message.
    • subscription.fullWsTransport: Boolean Enable sending every operation via WS.

  • persistedQueries: A hash/query map to resolve the full query text using it's unique hash. Overrides persistedQueryProvider.

  • onlyPersisted: Boolean. Flag to control whether to allow graphql queries other than persisted. When true, it'll make the server reject any queries that are not present in the persistedQueries option above. It will also disable any ide available (graphiql). Requires persistedQueries to be set, and overrides persistedQueryProvider.

  • persistedQueryProvider

    • isPersistedQuery: (request: object) => boolean: Return true if a given request matches the desired persisted query format.
    • getHash: (request: object) => string: Return the hash from a given request, or falsy if this request format is not supported.
    • getQueryFromHash: async (hash: string) => string: Return the query for a given hash.
    • getHashForQuery?: (query: string) => string: Return the hash for a given query string. Do not provide if you want to skip saving new queries.
    • saveQuery?: async (hash: string, query: string) => void: Save a query, given its hash.
    • notFoundError?: string: An error message to return when getQueryFromHash returns no result. Defaults to Bad Request.
    • notSupportedError?: string: An error message to return when a query matches isPersistedQuery, but returns no valid hash from getHash. Defaults to Bad Request.

  • allowBatchedQueries: Boolean. Flag to control whether to allow batched queries. When true, the server supports recieving an array of queries and returns an array of results.

  • compilerOptions: Object. Configurable options for the graphql-jit compiler. For more details check https://github.com/zalando-incubator/graphql-jit

queryDepth example

query {
  dogs {
    name
    owner {
      name
      pet {
        name
        owner {
          name
          pet {
            name
          }
        }
      }
    }
  }
}

A queryDepth of 6 would allow this query. 5 or less would throw with the error - unnamedQuery query exceeds the query depth limit of 5

HTTP endpoints

GET /graphql

Executed the GraphQL query passed via query string parameters. The supported query string parameters are:

  • query, the GraphQL query.
  • operationName, the operation name to execute contained in the query.
  • variables, a JSON object containing the variables for the query.

POST /graphql

Executes the GraphQL query or mutation described in the body. The payload must conform to the following JSON schema:

{
  type: 'object',
  properties: {
    query: {
      type: 'string',
      description: 'the GraphQL query'
    },
    operationName: {
      type: 'string'
    },
    variables: {
      type: ['object', 'null'],
      additionalProperties: true
    }
  }
}

For code from example use:

curl -H "Content-Type:application/json" -XPOST -d '{"query": "query { add(x: 2, y: 2) }"}' http://localhost:3000/graphql

POST /graphql with Content-type: application/graphql

Executes the GraphQL query or mutation described in the body. operationName and variables can not be passed using this method. The payload contains the GraphQL query.

For code from example use:

curl -H "Content-Type:application/graphql" -XPOST -d "query { add(x: 2, y: 2) }" http://localhost:3000/graphql

GET /graphiql

Serves GraphiQL if enabled by the options.

Decorators

mercurius adds the following decorators.

app.graphql(source, context, variables, operationName)

Decorate Server with a graphql method. It calls the upstream graphql() method with the defined schema, and it adds { app } to the context.

const Fastify = require('fastify')
const mercurius = require('mercurius')

const app = Fastify()
const schema = `
  type Query {
    add(x: Int, y: Int): Int
  }
`

const resolvers = {
  Query: {
    add: async (_, { x, y }) => x + y
  }
}

app.register(mercurius, {
  schema,
  resolvers
})

async function run() {
  // needed so that graphql is defined
  await app.ready()

  const query = '{ add(x: 2, y: 2) }'
  const res = await app.graphql(query)

  console.log(res)
  // prints:
  //
  // {
  //   data: {
  //      add: 4
  //   }
  // }
}

run()

app.graphql.extendSchema(schema), app.graphql.defineResolvers(resolvers) and app.graphql.defineLoaders(loaders)

It is possible to add schemas, resolvers and loaders in separate fastify plugins, like so:

const Fastify = require('fastify')
const mercurius = require('mercurius')

const app = Fastify()
const schema = `
  type Human {
    name: String!
  }

  type Dog {
    name: String!
    owner: Human
  }

  extend type Query {
    dogs: [Dog]
    add(x: Int, y: Int): Int
  }
`

const dogs = [
  { name: 'Max' },
  { name: 'Charlie' },
  { name: 'Buddy' },
  { name: 'Max' }
]

const owners = {
  Max: {
    name: 'Jennifer'
  },
  Charlie: {
    name: 'Sarah'
  },
  Buddy: {
    name: 'Tracy'
  }
}

const resolvers = {
  Query: {
    dogs: async (_, args, context, info) => dogs,
     add: async (_, { x, y }) => x + y
  }
}

const loaders = {
  Dog: {
    async owner(queries, { reply }) {
      return queries.map(({ obj }) => owners[obj.name])
    }
  }
}

app.register(mercurius)

app.register(async function (app) {
  app.graphql.extendSchema(schema)
  app.graphql.defineResolvers(resolvers)
  app.graphql.defineLoaders(loaders)
})

async function run() {
  // needed so that graphql is defined
  await app.ready()

  const query = '{ add(x: 2, y: 2) }'
  const res = await app.graphql(query)

  console.log(res)
  // prints:
  //
  // {
  //   data: {
  //      add: 4
  //   }
  // }
}

run()

app.graphql.replaceSchema(schema)

It is possible to replace schema and resolvers using makeSchemaExecutable function in separate fastify plugins, like so:

const Fastify = require('fastify')
const mercurius = require('mercurius')
const { makeExecutableSchema } = require('@graphql-tools/schema')

const app = Fastify()

app.register(mercurius, {
  schema: makeExecutableSchema({
    typeDefs: `
    type Query {
      add(x: Int, y: Int): Int
    }
  `,
    resolvers: {
      Query: {
        add: async (_, { x, y }) => x + y
      }
    }
  })
})

app.register(async function (app) {
  app.graphql.replaceSchema(
    makeExecutableSchema({
      typeDefs: `
      type Query {
        add(x: Int, y: Int, z: Int): Int
      }
    `,
      resolvers: {
        Query: {
          add: async (_, { x, y, z }) => x + y + z
        }
      }
    })
  )
})

async function run() {
  // needed so that graphql is defined

  await app.ready()

  const query = '{ add(x: 2, y: 2, z: 2) }'
  const res = await app.graphql(query)

  console.log(res)
  // prints:
  //
  // {
  //   data: {
  //      add: 6
  //   }
  // }
}

run()

app.graphql.transformSchema(transforms)

transforms can be an array of functions or a single function that accept the schema and returns a schema. It is an utility function that calls replaceSchema underneath.

app.graphql.extendSchema(typeDefs)
app.graphql.defineResolvers(resolvers)
app.graphql.transformSchema(directive()) // or [directive()]

app.graphql.schema

Provides access to the built GraphQLSchema object that mercurius will use to execute queries. This property will reflect any updates made by extendSchema or replaceSchema as well.

reply.graphql(source, context, variables, operationName)

Decorate Reply with a graphql method. It calls the upstream graphql() function with the defined schema, and it adds { app, reply } to the context.

const Fastify = require('fastify')
const mercurius = require('mercurius')

const app = Fastify()
const schema = `
  type Query {
    add(x: Int, y: Int): Int
  }
`

const resolvers = {
  add: async ({ x, y }) => x + y
}

app.register(mercurius, {
  schema,
  resolvers
})

app.get('/', async function (req, reply) {
  const query = '{ add(x: 2, y: 2) }'
  return reply.graphql(query)
})

async function run() {
  const res = await app.inject({
    method: 'GET',
    url: '/'
  })

  console.log(JSON.parse(res.body), {
    data: {
      add: 4
    }
  })
}

run()

Errors

Mercurius help the error handling with two useful tools.

  • ErrorWithProps class
  • ErrorFormatter option

ErrorWithProps

ErrorWithProps can be used to create Errors to be thrown inside the resolvers or plugins.

it takes 3 parameters:

  • message
  • extensions
  • statusCode
'use strict'

throw new ErrorWithProps('message', {
    ...
}, 200)

Extensions

Use errors extensions to provide additional information to query errors

GraphQL services may provide an additional entry to errors with the key extensions in the result.

'use strict'

const Fastify = require('fastify')
const mercurius = require('mercurius')
const { ErrorWithProps } = mercurius

const users = {
  1: {
    id: '1',
    name: 'John'
  },
  2: {
    id: '2',
    name: 'Jane'
  }
}

const app = Fastify()
const schema = `
  type Query {
    findUser(id: String!): User
  }

  type User {
    id: ID!
    name: String
  }
`

const resolvers = {
  Query: {
    findUser: (_, { id }) => {
      const user = users[id]
      if (user) return users[id]
      else
        throw new ErrorWithProps('Invalid User ID', {
          id,
          code: 'USER_ID_INVALID',
          timestamp: Math.round(new Date().getTime() / 1000)
        })
    }
  }
}

app.register(mercurius, {
  schema,
  resolvers
})

app.listen({ port: 3000 })

Status code

To control the status code for the response, the third optional parameter can be used.

throw new mercurius.ErrorWithProps('Invalid User ID', {moreErrorInfo})
// using the defaultErrorFormatter, the response statusCode will be 200 as defined in the graphql-over-http spec

throw new mercurius.ErrorWithProps('Invalid User ID', {moreErrorInfo}, 500)
// using the defaultErrorFormatter, the response statusCode will be 500 as specified in the parameter

const error = new mercurius.ErrorWithProps('Invalid User ID', {moreErrorInfo}, 500)
error.data = {foo: 'bar'}
throw error
// using the defaultErrorFormatter, the response status code will be always 200 because error.data is defined

Error formatter

Allows the status code of the response to be set, and a GraphQL response for the error to be defined. You find out how to do this here.

By default uses the defaultErrorFormatter, but it can be overridden in the mercurius options changing the errorFormatter parameter.

Important: using the default formatter, when the error has a data property the response status code will be always 200

While using custom error formatter, you can access the status code provided by the ErrorWithProps object via originalError property. Please keep in mind though, that originalError is a non-enumerable property, meaning it won't get serialized and/or logged as a whole.

app.register(mercurius, {
    schema,
    resolvers,
    errorFormatter: (result) => ({ statusCode: result.errors[0].originalError.statusCode, response: result })
})