Scala + Caliban で作るGraphQL バックエンド / Making GraphQL Backend with Scala + Caliban

Transcript

1. 阿川 耕司
   Scala + Caliban で作る
   GraphQL バックエンド
   

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2. 小売向けサイネージのプロダクト「ミライネージ」
   でテックリードを担当している。
   阿川 耕司 / Koji AGAWA
   2013年度 中途入社
   AI事業本部 DX本部 ミライネージ
   @atty303
   @atty303
   

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3. Scala + Caliban で作る
   GraphQL バックエンド
   

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4. 1.What's GraphQL ?
   2.Caliban
   3.Authentication
   4.Node Interface
   5.Relay-based Pagination
   6.Summary
   

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5. What’s GraphQL ?
   

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6. GraphQL
   •APIのクエリ言語
   •サーバーは型付きスキーマを公開
   •クライアントは欲しいデータだけをリクエスト
   •クライアントとサーバーは任意の言語を使える
   •サポートツールが充実
   

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7. GraphQL in Scala
   Sangria Caliban
   Since 2015 2019
   Effect System Future ZIO
   Boilerplate 多い 少ない
   Resolver 密結合 疎結合
   

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8. Caliban
   

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9. Caliban の特徴
   •最小限のボイラープレート
   •Purely Functional
   •強い型付け
   •明示的なエラー
   •スキーマとリゾルバーの分離
   

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10. case class User(
    id: UUID,
    name: String,
    age: Option[Int]
    )
    スキーマ定義
    type User {
    id: ID!
    name: String!
    age: Int
    }
    

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11. case class UserArgs(id: UUID)
    case class Query(
    user: UserArgs => Option[User],
    users: Seq[User]
    )
    スキーマ定義
    type Query {
    user(id: ID): User
    users: [User!]!
    }
    

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12. trait UserResolver {
    def getUser(id: UUID): Option[User]
    def getAllUsers(): Seq[User]
    }
    val query = Query(
    args => userResolver.getUser(args.id),
    userResolver.getAllUsers
    )
    val api = graphQL(RootResolver(query))
    リゾルバ定義
    

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13. query {
    user(id: 123) {
    name
    groups {
    name
    }
    }
    }
    N+1 問題
    

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14. for {
    user <- getUser(id)
    groups <- ZIO.foreachPar(user.groupIds)(getGroup)
    } yield User(user.name, groups)
    素朴な実装
    N+1 Query
    

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15. for {
    user <- getUser(id)
    groups <- ZQuery.foreachPar(user.groupIds)(getGroup)
    } yield User(user.name, groups)
    ZQuery
    1+1 Query
    

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16. case class GetGroup(id: Int) extends Request[Throwable, Group]
    val GroupDataSource =
    DataSource.fromFunctionBatchedM("GroupDataSource")(
    requests => dao.getGroups(requests.map(_.id))
    )
    def getGroup(id: Int): ZQuery[Any, Throwable, Group] =
    ZQuery.fromRequest(GetGroup(id))(GroupDataSource)
    ZQuery
    

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17. ZQuery のメリット
    •並列クエリ
    •同一クエリのキャッシュ(重複排除)
    •バッチ化
    DataLoader の FP アプローチ
    

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18. Authentication
    

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19. val routesM: IO[HttpRoutes[RIO[AppEnv, *]]] =
    for {
    a = Http4sAdapter.makeHttpService
    [AppEnv with Has[Auth.Service], CalibanError](interpreter)
    route = new Auth[AppEnv].apply(a)
    } yield Router[RIO[AppEnv, *]](
    "/graphql" -> route
    )
    http4s router
    

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20. class Auth[R <: Has[_] with Database]() {
    def apply(route: HttpRoutes[RIO[R with Has[Auth.Service, *]]): HttpRoutes[RIO[R, *]] =
    Http4sAdapter.provideSomeLayerFromRequest[R with Database, Has[Auth.Service]](
    route,
    req => makeService(req).toLayer
    )
    def makeService(req: Request[RIO[R, *]]): RIO[Database, Auth.Service] = ???
    }
    object Auth {
    trait Service {
    def authUser: Option[AuthUser]
    }
    }
    Authentication service
    

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21. case class Query(
    getAllUsers: ZIO[Has[Auth.Service], Throwable, User]
    )
    val resolver = Query(
    ZIO.access[Has[Auth.Service]] {
    _.get.authUser match {
    case Some(authUser) => ???
    case None => ???
    }
    )
    Usage
    

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22. Authentication
    •ZLayerの理解が必須
    •サンプルが解読できずDiscordで作者に聞いた
    •ZIO コミュニティDiscordは活発
    

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23. Node Interface
    

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24. # An object with a Globally Unique ID
    interface Node {
    # The ID of the object.
    id: ID!
    }
    type User implements Node {
    id: ID!
    # Full name
    name: String!
    }
    Node Interface
    

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25. sealed trait Node {
    def id: String
    }
    case class User(id: String, name: String) extends Node
    Node Interface in Caliban (?)
    

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26. sealed trait Node {
    def id: String
    }
    case class User(id: String, name: String) extends Node
    Not scalable ...
    

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27. def lookupUser(id: String): UQuery[Option[User]] =
    ZQuery.some(User(id))
    def lookupGroup(id: String): UQuery[Option[Group]] =
    ZQuery.some(Group(id))
    val node = Node.instance
    .withType(lookupUser)
    .withType(lookupGroup)
    implicit val nodeSchema: Schema[Any, Node] = node.build
    case class Query(
    node: NodeArg => IO[CalibanError, Node]
    )
    Solution
    

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28. Solution
    https://gist.github.com/paulpdaniels/d8e932b9faee19812d2de8f56dd77a51
    

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29. Node Interface
    •Caliban標準のサポート無し
    •サンプル実装をベースに独自実装
    

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30. Relay-based Pagination
    

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31. object PaginatedQuery {
    def apply[A: Get](
    fullTableQuery: Fragment
    )(
    cursor: Cursor,
    orderBy: Fragment = Fragment.empty
    ): TranzactIO[PageInfoDto[A]] = ???
    }
    Relay-based Pagination の一般化
    

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32. case class Cursor(
    first: Option[Int],
    after: Option[String],
    last: Option[Int],
    before: Option[String]
    )
    Cursor / PageInfo
    case class PageInfoDto[A](
    totalCount: Long,
    hasPreviousPage: Boolean,
    hasNextPage: Boolean,
    value: Vector[A]
    )
    

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33. WITH _SOURCE AS ($table),
    _T AS (
    SELECT ROW_NUMBER() OVER (ORDER BY ${orderBy}) AS n, ${idColumn} AS id
    FROM _SOURCE
    ORDER BY ${orderBy}
    ),
    _afterN AS (SELECT n FROM _T WHERE _T.id = ${after}),
    _beforeN AS (SELECT n FROM _T WHERE _T.id = ${before}),
    _totalN AS (SELECT COUNT(1) AS total FROM _T),
    _page AS (
    SELECT n, _T.id
    FROM _T
    WHERE (${cursor.after} IS NULL OR n > COALESCE((TABLE _afterN), 0))
    AND (${cursor.first} IS NULL OR n <= COALESCE((TABLE _afterN), 0) + ${cursor.first})
    AND (${cursor.before} IS NULL OR n < COALESCE((TABLE _beforeN), (TABLE _totalN) + 1))
    AND (${cursor.last} IS NULL OR n >= COALESCE((TABLE _beforeN), (TABLE _totalN) + 1) - ${cursor.last})
    ),
    _minN AS (SELECT MIN(n) FROM _page),
    _maxN AS (SELECT MAX(n) FROM _page)
    SELECT
    _totalN.total,
    CASE WHEN (TABLE _minN) > 1 THEN true ELSE false END AS has_previous_page,
    CASE WHEN (TABLE _maxN) < (TABLE _totalN) THEN true ELSE false END AS has_next_page,
    _page.id
    FROM _page, _totalN
    Pagination SQL (!)
    

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34. WITH _SOURCE AS ($table),
    …
    [$table]
    SELECT id FROM signages ORDER BY name
    Pagination SQL
    

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35. val nodes = ZQuery.foreachPar(
    pageInfo.value.map(id => GetSignageRequest(GRI(id.asString)))
    )(
    ZQuery.fromRequest(_)(getSignageDataSource.dataSource)
    )
    SignageConnection(
    edges = nodes.map(_.map(n => SignageEdge(n.databaseId.asString, n))),
    nodes = nodes,
    pageInfo = PageInfo(
    hasNextPage = pageInfo.hasNextPage,
    hasPreviousPage = pageInfo.hasPreviousPage,
    startCursor = pageInfo.value.headOption.map(_.asString),
    endCursor = pageInfo.value.lastOption.map(_.asString)
    ),
    totalCount = pageInfo.totalCount
    )
    Resolver
    

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36. ミライネージの Pagination
    •Pagination の一般化
    •ページングしない、IDだけを返すSQLだけ書く
    •ZQueryによりIDを肉付けする
    

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37. Summary
    

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38. GraphQLで得られたもの
    •フロントエンドに依存しすぎないバックエンド
    (CQRSではフロントエンドにあわせて都度Queryを実装)
    •Vue Apollo でフロントエンドの爆速実装
    •graphql-code-generator で型安全なクエリ
    •安定したモデル (≠ ドメインモデル)
    

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39. Summary
    •型安全&ボイラープレート無しの GraphQL バックエンド
    •純粋関数による構成からのテスト容易性
    •標準仕様への準拠からの言語間の相互運用性
    •責務の分離による記述の容易性
    

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40. ご視聴ありがとうございました。
    

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