Rails サービスレイヤー設計の実践ガイド

# コントローラがシンプルになる
class OrdersController < ApplicationController
  def create
    result = Orders::CreateService.call(
      user: current_user,
      cart: current_cart
    )

    if result.success?
      redirect_to result.order
    else
      render :new, alert: result.error
    end
  end
end

# app/services/sync/synchronizer.rb
module Sync
  class Synchronizer
    def initialize(workspace)
      @context = Context.new(workspace)
      @file_processor = FileProcessor.new(@context)
      @refresher = WorkspaceRefresher.new(@context)
      @notifier = Notifier.new(@context)
    end

    def self.call(workspace)
      new(workspace).call
    end

    def call
      ActiveRecord::Base.transaction do
        file_processor.process
        refresher.refresh
      end
    ensure
      notifier.notify
    end

    private

    attr_reader :context, :file_processor, :refresher, :notifier
  end
end

# 何をするか分からない
WorkspaceRepositories::Sync::Main

# 同期処理であることが明確
WorkspaceRepositories::Sync::Synchronizer

# より簡潔に
WorkspaceRepositories::Synchronizer

# Context なし: 同じ引数を何度も渡す
def call
  file_processor.process(workspace, github_repo, recorder)
  refresher.refresh(workspace, github_repo, recorder)
  notifier.notify(workspace, github_repo, recorder)
end

# Context あり: 共有状態をまとめる
def call
  file_processor.process
  refresher.refresh
  notifier.notify
end

# app/services/sync/context.rb
module Sync
  class Context
    attr_reader :workspace, :github_repo, :recorder

    def initialize(workspace, recorder:)
      @workspace = workspace
      @github_repo = workspace.github_repo
      @recorder = recorder
    end
  end
end

class FileProcessor
  def initialize(context)
    @context = context
  end

  def process
    # context.workspace, context.github_repo にアクセス
  end
end

class Context
  attr_reader :workspace, :github_repo, :recorder

  def initialize(workspace, recorder:)
    @workspace = workspace
    @github_repo = workspace.github_repo
    @recorder = recorder
    freeze  # 初期化後は状態変更不可
  end
end

# 良い例: 依存関係が明確
context = Context.new(workspace, recorder: recorder)

# 避ける例: 後から setter で注入（状態変更につながる）
context = Context.new(workspace)
context.recorder = recorder

# 遅延初期化の例: 必要になったときだけ計算
def github_app
  @github_app ||= github_repo&.github_app
end

class Synchronizer
  def initialize(workspace)
    # HistoryRecorder を先に作成
    @recorder = HistoryRecorder.new(workspace)

    # Context を immutable で作成（recorder を注入）
    @context = Context.new(workspace, recorder: @recorder)

    # その他のサービスを初期化
    @config_handler = ConfigurationHandler.new(@context)
    @file_processor = FileProcessor.new(@context)
    @refresher = WorkspaceRefresher.new(@context)
    @notifier = Notifier.new(@context)
  end

  def call
    return if skip?

    @recorder.create_start_history

    ActiveRecord::Base.transaction do
      @config_handler.save_settings
      @file_processor.process
      @refresher.refresh
    end
  rescue => e
    @recorder.add_error(e)
    raise
  ensure
    @recorder.save
    @notifier.notify
  end
end

# 結果が不明確
def process_files
  @path_checksums = []
  @tree_file_paths = []
  # ...
  # 呼び出し元は @path_checksums や @tree_file_paths に直接アクセス
end

# 使い方が不自然
processor = FileProcessor.new(context)
processor.process_files
refresher.delete_unused_paths(processor.path_checksums)  # 内部状態に依存

# 結果が構造化される
ProcessResult = Struct.new(:path_checksums, :tree_file_paths, keyword_init: true) do
  def processed_count
    path_checksums.length
  end
end

def process_files
  # ... 処理 ...
  ProcessResult.new(
    path_checksums: @path_checksums,
    tree_file_paths: @tree_file_paths
  )
end

# 使い方が明確
result = processor.process_files
refresher.delete_unused_paths(result.path_checksums)  # 結果オブジェクト経由

class FileProcessor
  # ファイル処理結果を表す Struct
  ProcessResult = Struct.new(
    :path_checksums,
    :tree_file_paths,
    keyword_init: true
  ) do
    # ヘルパーメソッドも追加可能
    def processed_count
      path_checksums.length
    end

    def any_paths?
      path_checksums.any? || tree_file_paths.any?
    end
  end

  def process_files
    files = collect_files
    prefetch_commit_times(files)
    save_files(files)

    ProcessResult.new(
      path_checksums: @path_checksums,
      tree_file_paths: @tree_file_paths
    )
  end
end

# シンプルな成功・失敗パターン
Result = Struct.new(:success?, :value, :error, keyword_init: true) do
  def initialize(success: true, value: nil, error: nil)
    super(success?, value, error)
  end
end

# または専用クラス
class ProcessResult
  attr_reader :status, :data, :error

  def initialize(status, data = nil, error = nil)
    @status = status
    @data = data
    @error = error
  end

  def success?
    status == :success
  end

  def failed?
    status == :failure
  end
end