Add reactivity to an existing source using GraphQL Mesh

Jean-Yves CouëtTuesday, Dec 15th 2020

Introduction

Working on the code generator for svelte plugin, I was looking for a public graphQL endpoint having queries, mutations and subscriptions for nice examples. Unfortunately I didn’t find anything out of the box, ready to use for my demos. So I decided to extend an existing source!

Starting Point

Across my researches I found one cool public endpoint regarding SpaceX. It has Queries and Mutations ready to use! So I decided to pimp this endpoint, and bring a bit of reactivity with subscriptions.

The idea is to publish the new user when it’s inserted with this mutation:

mutation addUser {
  insert_users(objects: { name: "jyc" }) {
    affected_rows
    returning {
      name
    }
  }
}

🏎

How hard is to do this? Let’s find out… Let’s Pimp this GraphQL!

Implementation

Multiple ways are possible!

Spoiler alert

Thanks to graphql-mesh, it’s dead easy! 🚀🚀🚀

1. Create a New Repo

mkdir newRepo
cd newRepo
yarn init

2. Add `graphql-mesh` Packages

yarn add @graphql-mesh/cli @graphql-mesh/graphql @graphql-mesh/transform-resolvers-composition graphql

3. Add `.meshrc.yaml` File in the Root Folder With

.meshrc.yaml

sources:
  - name: spacexGQL
    handler:
      graphql:
        endpoint: https://api.spacex.land/graphql/
 
additionalTypeDefs: |
  extend type Subscription {
    usersAdded: [users]
  }
 
transforms:
  - resolversComposition:
      - resolver: 'Mutation.insert_users'
        composer: ./src/composition/insert_user
 
additionalResolvers:
  - type: Subscription
    field: usersAdded
    pubsubTopic: usersAdded

Where I

declare the graphQL source
extend Subscription to listen to user added users
compose the existing Mutation.insert_users

4. Add `./src/composition/insert_user.js` File with All the Logic for This New Mutation Composition

insert_user.js

module.exports = next => async (root, args, context, info) => {
  // add returning.id to the selection
  info.operation.selectionSet.selections[0].selectionSet.selections.push({
    kind: 'Field',
    name: {
      kind: 'Name',
      value: 'returning'
    },
    arguments: [],
    directives: [],
    selectionSet: {
      kind: 'SelectionSet',
      selections: [
        {
          kind: 'Field',
          name: {
            kind: 'Name',
            value: 'id'
          },
          arguments: [],
          directives: []
        }
      ]
    }
  })
 
  // send the mutation to the graphQL source
  const result = await next(root, args, context, info)
 
  // select returned ids
  const ids = result.returning.map(c => c.id)
 
  // Query users enforcing fields to return
  const responseUser = await context.spacexGQL.apiQuery.users(
    {
      where: { id: { _in: ids } }
    },
    {
      fields: {
        id: true,
        name: true,
        rocket: true,
        timestamp: true,
        twitter: true
      }
    }
  )
 
  // publish new users
  context.pubsub.publish('usersAdded', responseUser)
 
  return result
}

That’s it!

Wrap Up

Extending an endpoint with subscription is easy! Thx to tooling.
You can find the source on GitHub
You see all this in action directly in the playground

I’m now ready to work on the demo for Svelte Codegen! Stay tunned ;)

@jycouet

💡

Special thanks to n1ru4l who helped me find the nicest way to do it ;)

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