Introduction to GraphQL in Scala

Yuki KatadaScalaMatsuri 2017

Scalaで始める GraphQL

About MeName

• Yuki Katada (片田雄樹 )

Affiliation

• CyberAgent, Inc.

• Media Development Headquarters (メディアディベロップメント事業本部 )

Scala Experience

• One and a half years

Follow Me

• On Twitter @ponyoky ← very few ppl are following me :(自己紹介

Our Job

• We are developing Advertising Network, which delivers Ads to

multiple media such as CyberAgent “Ameba”.

• Approximate 700 users are using our product.

• Our product has more than 600 million incoming traffics per day

• We are using GraphQL at Admin Page, which requires complex

queries

我々のプロダクトは Amebaメディアに対する広告を配信するシステムで、その管理画面部分で GraphQLを使用しています。

What is GraphQL?

GraphQLとは？

What is GraphQL?GraphQL is a query language, which is developed by Facebook.

It provides an alternative to REST. (Not Graph DB)

Some GraphQL libraries are provided as following:

• Javascript

• Python

• Scala

• and more.

GraphQLとは RESTの代替としての立ち位置のクエリ言語です。

Why GraphQL?

なぜ GraphQLなのか？

Multiple requests in REST

Endpoints/users/books

/companies...

I want resources at “/users”

and“/books”

and“/companies”

REST

server client

database

UsersBooks

Companies

RESTでは複数リソースを取得するために複数のリクエストが必要となります。

Multiple requests in REST

Resources

Users

Books

Companies

/users

/books

/companies

Endpoints

複数のリソースに対して複数のエンドポイントが紐付いています。

REST

REST requires n requests to retrieve n different resources.So if website required 100 different resources…?

RESTでは大量のリクエストが発生する可能性がある。

Single request in GraphQL

Endpoint/graphql

I want resources at “/users”

and“/books”

and“/companies”

GraphQL

server client

database

UsersBooks

Companies

GraphQLでは単一のリクエストのみで複数のリソースが取得できます。

Single request in GraphQL

Resources

Users

Books

Companies

/graphql

Endpoint

“query” : “{ user book company }”

Request Body

なので、 1つのエンドポイントに複数のリソースが紐付いている状態です。

GraphQL

GraphQL in Scala

Scalaでの GraphQL

GraphQL library for Scala

Sangria● The most famous Scala GraphQL library

● Github Repo

○ https://github.com/sangria-graphql/sangria

● There is an awesome documentation

○ http://sangria-graphql.org/

Scalaで実装された GraphQLライブラリ「 Sangria」

In my example, I prepared dummy data.

These resources are same as a previous example; users, books, and companies

In general, DummyData would be a database or data source.

DummyData.scala

今回の例では、ダミーデータを使用した例で説明します。

In DummyDataRepo class, I defined 3 methods to retrieve each resource.

DummyRepo.scala

ダミーデータを取得するレポジトリクラスを定義します。

GraphQLの根幹となる、オブジェクト構造を定義したクラスの例です。

This is SchemaDefinition object, which defines Single Endpoint, Arguments, and Object Structures.

In GraphQL, we have to define Object Structures to map onto query AST of request body.

SchemaDefinition.scala

When you retrieve resources from this API, you need to access in HTTP Post method. In this example, I requests user data with id = 1, and the right side JSON shows response.

GraphQLクエリで APIリクエストした場合の例です。

Please look at my sample code on Github for more detail.

https://github.com/yuki-katada/scalamatsuri_sangria

詳細は Githubを参照してください。

Pros/Cons

実際に使ってみて見えてきた長所と短所

Pros

• Less HTTP requests (less API access) compared to REST

• Additional server side implementation is not required in many cases

– Only client side modification to GraphQL query is required

• GraphiQL makes tests/debugs easier

– An interactive in-browser IDE for GraphQL

長所

Cons

• It is very hard to design Domain-Specific architecture

• Client Side is required to write very long request body

– Who wants to write string formatted & type-unsafe request body…?

• Many people struggle with GraphQL query

– It is hard to understand for many people

短所

Result

Cons are too critical compared to pros…

So we decided to replace GraphQL with REST :(

結果

Thank you for listening :)