Code Reading - Learn ❤️ GraphQL

Published Thursday, June 22, 2017

Notes from Flatiron School engineering team’s code reading on using GraphQL with our core codebase.

What is GraphQL?

• “Graph Query Language”
• Alternative to REST pattern
• Making your data queryable through a single endpoint

Why use GraphQL?

• More declarative
• More consumer focused
• Simplified endpoints
• Fewer requests
  • With REST, request count grows w/ more data you need
  • With GraphQL, only request as much data as you need => more efficient

In use in the wild

• GitHub API
• Shopify

Stuff to Think About

• Due to HTML limitations, super long queries get sent via POST request
• Mutations

Demo

1. Spin up new rails app: rails new graphql-demo
2. Add graphql-ruby gem to Gemfile
3. Run rails generate graphql:install
   • gives you graphql directory with sub-directories for mutations, types, new controller, new route graphql-rails
4. Lookit /grpahiql loader dev tool
5. Lookit /app/graphql/graphql_demo_schema.rb
6. Lots of demo boilerplate-y examples generated for us
7. Add more field queries to Types::QueryType

  field :course, Types::CourseType do
    description "This will return a single course"
    argument :id, !types.Int # bang means required
    resolve->(obj, args, ctx){
      Course.find(args["id"])
    }
  end

  field :customString, types.String do
    description "This will return a custom string"
    resolve->(obj, args, ctx){
      "custom string"
    }
  end

1. Define types in /graphql/types dir

  Types::CourseType = GraphQL::ObjectType.define do
    name "Course"
    field :name, types.String
    field :description, types.String
  end

  Types::StudentType = GraphQL::ObjectType.define do
    name "Student"
    field :first_name, types.String
    field :last_name, types.String
  end

1. Make the request

  {
    course(id: 1) {
      name
      description
    }
    student(id: 2) {
      first_name
    }
  }

1. Note: doesn’t handle 404s very gracefully. Tries to parse error message as JSON, so you end up w/ strange error responses
2. How to do associations

  # type
  Types::CourseType = GraphQL::ObjectType.define do
    name "Course"
    field :name, types.String
    field :description, types.String
    field :students, Types::StudentType.to_list_type
      resolve -> (obj, args, ctx) {
        obj.students
      }
  end

  # request
  {
    course(id: 1) {
      name
      students {
        first_name
        last_name
      }
    }
  }