Beyond REST: GraphQL in Ruby on Rails

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Vipul A M GRAPHQL BEYOND REST

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@vipulnsward Saeloun

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https://blog.saeloun.com/

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Kyoto Typhoon last year

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Alaska 7.2 Earthquake from 9th Floor

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NY Manhattan Blackout

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Stabbings in Singapore

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GRAPHQL

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-2012/2015 -N+1 HTTP Queries -Under/Over querying -Versioning

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-Supporting Multiple Apis:  api/v1, api/mobile, api/v2  api/v42?, etc

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QUICK TOUR

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BEFORE

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GRAPHQL RUBY

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-Schema -Queries -Mutations -Subscriptions

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# Add graphql-ruby boilerplate and mount graphiql in development rails g graphql:install # Make your first object type rails g graphql:object Post title:String rating:Int comments:[Comment]

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# app/graphql/types/post_type.rb class Types::PostType < Types::BaseObject field :id, ID, null: false field :title, String, null: false field :truncated_preview, String, null: false field :comments, [Types::CommentType], null: true end

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class QueryType < GraphQL::Schema::Object description "The query root of this schema" # First describe the field signature: field :post, PostType, null: true do description "Find a post by ID" argument :id, ID, required: true end # Then provide an implementation: def post(id:) Post.find(id) end end

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class Schema < GraphQL::Schema query QueryType end

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query_string = " { post(id: 1) { id title truncatedPreview } }" result_hash = Schema.execute(query_string) # { # "data" => { # "post" => { # "id" => 1, # "title" => "GraphQL is nice" # "truncatedPreview" => "GraphQL is..." # } # } # }

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SCHEMA / TYPES

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type User { email: String handle: String! friends: [User!]! } GraphQL Schema Deﬁnition Language(SDL)

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class Types::User < GraphQL::Schema::Object field :email, String, null: true field :handle, String, null: false field :friends, [User], null: false end

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class Types::TodoList < Types::BaseObject field :name, String, null: false field :is_completed, String, null: false # Related Object: field :owner, Types::User, null: false # List field: field :viewers, [Types::User], null: false # Connection/for pagination-relay: field :items, Types::TodoItem.connection_type, null: false do argument :status, TodoStatus, required: false end end

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class ChangelogSchema < GraphQL::Schema mutation(Types::MutationType) query(Types::QueryType) end

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SCALAR field :name, String field :top_score, Integer, null: false field :avg_points_per_game, Float, null: false field :is_top_ranked, Boolean, null: false field :id, ID, null: false field :created_at, GraphQL::Types::ISO8601DateTime, null: false field :parameters, GraphQL::Types::JSON, null: false CustomScalars

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ENUMS class Types::MediaCategory < Types::BaseEnum value "AUDIO", "An audio file, such as music or spoken word" value "IMAGE", "A still image, such as a photo or graphic" value "TEXT", "Written words" value "VIDEO", "Motion picture, may have audio" end

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LISTS argument :categories, [Types::PostCategory], required: false field :previous_employers, [Types::Employer, null: true], null: false

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-Input Objects -Interfaces -Unions -Directives

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QUERIES

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query_string = "{ ... }" MySchema.execute(query_string) # { # "data" => { ... } # }

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MySchema.multiplex([ {query: query_string_1}, {query: query_string_2}, {query: query_string_3}, ]) # [ # { "data" => { ... } }, # { "data" => { ... } }, # { "data" => { ... } }, # ]

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context = { current_user: current_user, routes: Rails.application.routes.url_helpers, } query_string = "{ ... }" MySchema.execute(query_string, context: context) # { # "data" => { ... } # }

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query_string = " query getPost($postId: ID!) { post(id: $postId) { title } }" variables = { "postId" => "1" } MySchema.execute(query_string, variables: variables)

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-root_value -operation_name -max_depth -max_complexity

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class Queries::Commit::Detail < Queries::BaseResolver type Types::CommitType, null: false argument :id, String, required: true def resolve(id:) Commit.find(id) rescue ActiveRecord::RecordNotFound => error GraphQL::ExecutionError.new(error.message) end end

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MUTATIONS

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class Schema < GraphQL::Schema # ... mutation(Types::Mutation) end

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-CRUD -Controller level operations -Session Management -File Creations, etc

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class Mutations::PublishCommit < Mutations::BaseMutation type Types::MutationResponseType argument :id, String, required: true argument :body, String, required: false def resolve(id:, body: nil) commit = Commit.find(id) create_or_update_post(body, commit) if body.present? commit.published! commit rescue ActiveRecord::RecordNotFound, ActiveRecord::RecordInvalid => error GraphQL::ExecutionError.new(error.message) end private def create_or_update_post(body, commit) post = Post.find_or_initialize_by(commit_id: commit.id) post.update body: body end end

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SUBSCRIPTIONS VIA ACTION CABLE

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VALIDATION -Client side validation -Server Query validation -Demo

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ERROR HANDLING -Query Validation Errors -Invariants: null ﬁelds, union/interface

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class Mutations::PublishCommit < Mutations::BaseMutation ... def resolve(id:, body: nil) commit = Commit.find(id) create_or_update_post(body, commit) if body.present? commit.published! commit rescue ActiveRecord::RecordNotFound, ActiveRecord::RecordInvalid => error raise GraphQL::ExecutionError.new(error.message) # OR raise GraphQL::ExecutionError.new(commit.full_messages.join(", ")) end end

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class Types::UserError < Types::BaseObject field :message, String, null: false field :path, [String], null: true end  class Mutations::UpdatePost < Mutations::BaseMutation # ... field :errors, [Types::UserError], null: false end 

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def resolve(id:, attributes:) post = Post.find(id) if post.update(attributes) { post: post, errors: [], } else # Convert Rails model errors into GraphQL-ready error hashes user_errors = post.errors.map do |attribute, message| path = ["attributes", attribute.camelize] { path: path, message: message, } end { post: post, errors: user_errors, } end end

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class ChangelogSchema < GraphQL::Schema ... rescue_from(ActiveRecord::NotFound) do |err, obj, args, ctx, field| # Raise a graphql-friendly error with a custom message raise GraphQL::ExecutionError, "#{field.type.unwrap.graphql_name} not found" end end

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INTROSPECTION -Demo -Visibility(Types/Mutations, etc) -Schema Driven Development

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LAZY EXECUTION -Object Store -shopify/graphql-batch -exAspArk/batch-loader -@defer

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class LazyFindPerson def initialize(query_ctx, person_id) @person_id = person_id @lazy_state = query_ctx[:lazy_find_person] ||= { pending_ids: Set.new, loaded_ids: {}, } @lazy_state[:pending_ids] << person_id end def person loaded_record = @lazy_state[:loaded_ids][@person_id] if loaded_record loaded_record else pending_ids = @lazy_state[:pending_ids].to_a people = Person.where(id: pending_ids) people.each { |person| @lazy_state[:loaded_ids][person.id] = person } @lazy_state[:pending_ids].clear @lazy_state[:loaded_ids][@person_id] end end end

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class MySchema < GraphQL::Schema # ... lazy_resolve(LazyFindPerson, :person) end field :author, PersonType, null: true def author LazyFindPerson.new(context, object.author_id) end     { p1: post(id: 1) { author { name } } p2: post(id: 2) { author { name } } p3: post(id: 3) { author { name } } }

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BATCHING -Client side: Demo -Multiplex -Dataloader

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CACHING -GraphQL preference: id, __typename -InMemoryStore in Apollo -Rails.cache -stackshareio/graphql-cache (easy caching on models) -CDN Caching(Akamai, etc)

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VERSIONING

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field :author_name, String, deprecation_reason: "Commit author can now be accessed as an Object", null: false DEPRECATIONS

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CONSIDERATIONS -JSON with GZIP -Pagination

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TRANSITION -Use Both: REST for Auth /  GraphQL -apollo-link-rest

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THANK YOU https://speakerdeck.com/vipulnsward/beyond-rest-graphql-in-ruby-on-rails