Outer_join.rb

This content was produced by an LLM and could include errors.

このスクリプトは配列同士の左外部結合です。users 各要素について user_id が一致する投稿を find で探し、見つかれば merge で title を統合します。投稿がないユーザー(Charlie)は title: nil のまま保持され、SQLの LEFT JOIN と同じ結果が得られます。

users = [
  { id: 1, name: 'Alice' },
  { id: 2, name: 'Bob' },
  { id: 3, name: 'Charlie' }
  ]
#=> [{id: 1, name: "Alice"}, {id: 2, name: "Bob"}, {id: 3, name: "Charlie"}]

posts = [
  { id: 1, user_id: 1, title: 'Post 1' },
  { id: 2, user_id: 2, title: 'Post 2' }
  ]
#=> [{id: 1, user_id: 1, title: "Post 1"}, {id: 2, user_id: 2, title: "Post 2"}]

users.map do |user|
  post = posts.find { |p| p[:user_id] == user[:id] }
  user.merge(post || { title: nil })
end
#=> [{id: 1, name: "Alice", user_id: 1, title: "Post 1"},
 {id: 2, name: "Bob", user_id: 2, title: "Post 2"},
 {id: 3, name: "Charlie", title: nil}]

Ruby 4.0.6