Ruby on Rails\u306e\u5f37\u529b\u306a\u6a5f\u80fd\u306e1\u3064\u3067\u3042\u308bjoin\u30e1\u30bd\u30c3\u30c9\u3002
\u9069\u5207\u306b\u4f7f\u7528\u3059\u308b\u3053\u3068\u3067\u3001\u8907\u96d1\u306a\u30c7\u30fc\u30bf\u64cd\u4f5c\u3092\u52b9\u7387\u7684\u306b\u884c\u3044\u3001\u30a2\u30d7\u30ea\u30b1\u30fc\u30b7\u30e7\u30f3\u306e\u30d1\u30d5\u30a9\u30fc\u30de\u30f3\u30b9\u3092\u5927\u5e45\u306b\u5411\u4e0a\u3055\u305b\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002
\u672c\u8a18\u4e8b\u3067\u306f\u3001join\u306e\u57fa\u790e\u304b\u3089\u9ad8\u5ea6\u306a\u4f7f\u7528\u6cd5\u307e\u3067\u3001\u5b9f\u8df5\u7684\u306a\u4f8b\u3092\u4ea4\u3048\u3066\u8a73\u3057\u304f\u89e3\u8aac\u3057\u307e\u3059\u3002<\/p>\n\n\n\n
\u76ee\u6b21 <\/p>\n
Ruby on Rails\u3067\u30c7\u30fc\u30bf\u30d9\u30fc\u30b9\u64cd\u4f5c\u3092\u884c\u3046\u969b\u3001\u8907\u6570\u306e\u30c6\u30fc\u30d6\u30eb\u304b\u3089\u5fc5\u8981\u306a\u60c5\u5831\u3092\u53d6\u5f97\u3059\u308b\u3053\u3068\u306f\u3088\u304f\u3042\u308a\u307e\u3059\u3002 ActiveRecord\u306e \u3067\u306f\u3001\u5177\u4f53\u7684\u306a\u30b3\u30fc\u30c9\u4f8b\u3092\u898b\u3066\u3044\u304d\u307e\u3057\u3087\u3046\u3002\u4ee5\u4e0b\u306e\u3088\u3046\u306a\u30e2\u30c7\u30eb\u304c\u3042\u308b\u3068\u3057\u307e\u3059\u3002<\/p>\n\n\n\n \u3053\u308c\u3089\u306e\u4f8b\u304b\u3089\u308f\u304b\u308b\u3088\u3046\u306b\u3001 \u5fdc\u7528\u4f8b\u3068\u3057\u3066\u3001\u6761\u4ef6\u4ed8\u304djoin\u3084\u30ab\u30b9\u30bf\u30e0SQL\u6587\u5b57\u5217\u3092\u4f7f\u7528\u3057\u305fjoin\u3082\u3042\u308a\u307e\u3059\u3002<\/p>\n\n\n\n \u30c7\u30fc\u30bf\u30d9\u30fc\u30b9\u64cd\u4f5c\u306b\u304a\u3044\u3066\u3001\u7570\u306a\u308b\u30c6\u30fc\u30d6\u30eb\u9593\u306e\u30c7\u30fc\u30bf\u3092\u7d50\u5408\u3059\u308b\u5fc5\u8981\u304c\u3057\u3070\u3057\u3070\u751f\u3058\u307e\u3059\u3002 \u3053\u308c\u3089\u306e\u7d50\u5408\u30bf\u30a4\u30d7\u3092\u9069\u5207\u306b\u4f7f\u3044\u5206\u3051\u308b\u3053\u3068\u3067\u3001\u5fc5\u8981\u306a\u30c7\u30fc\u30bf\u3092\u52b9\u7387\u7684\u306b\u53d6\u5f97\u3067\u304d\u307e\u3059\u3002 Ruby on Rails\u306f\u3001\u8907\u96d1\u306a\u7d50\u5408\u64cd\u4f5c\u3092\u30b7\u30f3\u30d7\u30eb\u306b\u5b9f\u73fe\u3059\u308b\u305f\u3081\u306e\u591a\u304f\u306e\u300c\u30de\u30b8\u30c3\u30af\u300d\u3092\u63d0\u4f9b\u3057\u3066\u3044\u307e\u3059\u3002<\/p>\n\n\n\n Rails\u306e\u30e2\u30c7\u30eb\u95a2\u9023\u4ed8\u3051\u3092\u5229\u7528\u3059\u308b\u3053\u3068\u3067\u3001\u8907\u96d1\u306aJOIN\u3092\u7c21\u5358\u306b\u8a18\u8ff0\u3067\u304d\u307e\u3059\u3002<\/p>\n\n\n\n \u8907\u6570\u306e\u6761\u4ef6\u3084\u7d50\u5408\u3092\u3001\u30e1\u30bd\u30c3\u30c9\u30c1\u30a7\u30fc\u30f3\u3092\u4f7f\u3063\u3066\u76f4\u611f\u7684\u306b\u8a18\u8ff0\u3067\u304d\u307e\u3059\u3002<\/p>\n\n\n\n \u3088\u308a\u8907\u96d1\u306a\u6761\u4ef6\u3084\u7d50\u5408\u304c\u5fc5\u8981\u306a\u5834\u5408\u3001Arel\u3068\u3044\u3046SQL\u30d3\u30eb\u30c0\u30fc\u30e9\u30a4\u30d6\u30e9\u30ea\u3092\u4f7f\u7528\u3067\u304d\u307e\u3059\u3002<\/p>\n\n\n\n \u3053\u308c\u3089\u306e\u30c6\u30af\u30cb\u30c3\u30af\u3092\u99c6\u4f7f\u3059\u308b\u3053\u3068\u3067\u3001\u8907\u96d1\u306a\u30c7\u30fc\u30bf\u30d9\u30fc\u30b9\u64cd\u4f5c\u3082\u8aad\u307f\u3084\u3059\u304f\u4fdd\u5b88\u6027\u306e\u9ad8\u3044\u30b3\u30fc\u30c9\u3067\u5b9f\u73fe\u3067\u304d\u307e\u3059\u3002<\/p>\n\n\n\n \u6b21\u306e\u30bb\u30af\u30b7\u30e7\u30f3\u3067\u306f\u3001 Ruby on Rails\u3067\u30c7\u30fc\u30bf\u30d9\u30fc\u30b9\u30af\u30a8\u30ea\u3092\u6700\u9069\u5316\u3059\u308b\u969b\u3001 \u307e\u305a\u3001 \u3053\u306e\u30b3\u30fc\u30c9\u306f\u3001\u6700\u521d\u306b\u3059\u3079\u3066\u306e\u30e6\u30fc\u30b6\u30fc\u3092\u53d6\u5f97\u3057\u3001\u305d\u306e\u5f8c\u30e6\u30fc\u30b6\u30fc\u3054\u3068\u306b\u6295\u7a3f\u6570\u3092\u53d6\u5f97\u3059\u308b\u305f\u3081\u306e\u30af\u30a8\u30ea\u3092\u5b9f\u884c\u3057\u307e\u3059\u3002 \u3053\u306e\u30b3\u30fc\u30c9\u3067\u306f\u3001\u30e6\u30fc\u30b6\u30fc\u3068\u6295\u7a3f\u306e\u30c7\u30fc\u30bf\u30921\u56de\u306e\u30af\u30a8\u30ea\u3067\u53d6\u5f97\u3057\u3001\u30e1\u30e2\u30ea\u4e0a\u306b\u4fdd\u6301\u3057\u307e\u3059\u3002 \u5834\u5408\u306b\u3088\u3063\u3066\u306f\u3001 \u3053\u306e\u30af\u30a8\u30ea\u306f\u3001\u516c\u958b\u3055\u308c\u305f\u6295\u7a3f\u3092\u6301\u3064\u30e6\u30fc\u30b6\u30fc\u3092\u53d6\u5f97\u3057\u3001\u540c\u6642\u306b\u305d\u308c\u3089\u306e\u30e6\u30fc\u30b6\u30fc\u306e\u6295\u7a3f\u30c7\u30fc\u30bf\u3082\u4e8b\u524d\u306b\u8aad\u307f\u8fbc\u307f\u307e\u3059\u3002 \u9069\u5207\u306b \u5b9f\u969b\u306e\u30a2\u30d7\u30ea\u30b1\u30fc\u30b7\u30e7\u30f3\u958b\u767a\u3067\u306f\u3001\u5358\u7d14\u306a1\u5bfe\u591a\u306e\u95a2\u4fc2\u3092\u8d85\u3048\u305f\u8907\u96d1\u306a\u30c7\u30fc\u30bf\u69cb\u9020\u306b\u76f4\u9762\u3059\u308b\u3053\u3068\u304c\u3088\u304f\u3042\u308a\u307e\u3059\u3002 \u591a\u5bfe\u591a\u95a2\u4fc2\u306f\u3001\u8907\u96d1\u306a\u30c7\u30fc\u30bf\u69cb\u9020\u306e\u4ee3\u8868\u7684\u306a\u4f8b\u3067\u3059\u3002\u4f8b\u3048\u3070\u3001\u30e6\u30fc\u30b6\u30fc\u3001\u6295\u7a3f\u3001\u30bf\u30b0\u306e\u95a2\u4fc2\u3092\u8003\u3048\u3066\u307f\u307e\u3057\u3087\u3046\u3002 \u3053\u306e\u3088\u3046\u306a\u95a2\u4fc2\u3092\u52b9\u7387\u7684\u306b\u6271\u3046\u306b\u306f\u3001\u4e2d\u9593\u30c6\u30fc\u30d6\u30eb\u3092\u4f7f\u7528\u3057\u305f \u3053\u306e\u4f8b\u3067\u306f\u3001 \u3088\u308a\u8907\u96d1\u306a\u6761\u4ef6\u3084\u96c6\u8a08\u3092\u5fc5\u8981\u3068\u3059\u308b\u5834\u5408\u3001\u30b5\u30d6\u30af\u30a8\u30ea\u3092\u4f7f\u7528\u3057\u305f\u9ad8\u5ea6\u306a \u4ee5\u4e0b\u306b\u3001\u904e\u53bb1\u30f6\u6708\u9593\u3067\u6700\u3082\u591a\u304f\u306e\u30b3\u30e1\u30f3\u30c8\u3092\u53d7\u3051\u53d6\u3063\u305f\u6295\u7a3f\u3092\u6301\u3064\u30e6\u30fc\u30b6\u30fc\u3092\u691c\u7d22\u3059\u308b\u4f8b\u3092\u793a\u3057\u307e\u3059\u3002<\/p>\n\n\n\n \u3053\u306e\u30af\u30a8\u30ea\u3067\u306f\u3001\u307e\u305a \u8907\u96d1\u306a \u8907\u96d1\u306a \u7d50\u5408\u306b\u4f7f\u7528\u3055\u308c\u308b\u30ab\u30e9\u30e0\u306b\u306f\u30a4\u30f3\u30c7\u30c3\u30af\u30b9\u3092\u4ed8\u4e0e\u3057\u3001\u30af\u30a8\u30ea\u306e\u5b9f\u884c\u901f\u5ea6\u3092\u5411\u4e0a\u3055\u305b\u307e\u3059\u3002<\/p>\n\n\n\n \u8907\u96d1\u306a\u30af\u30a8\u30ea\u306f
\u305d\u3093\u306a\u6642\u306b\u529b\u3092\u767a\u63ee\u3059\u308b\u306e\u304cjoin<\/code>\u30e1\u30bd\u30c3\u30c9\u3067\u3059\u3002
\u3053\u306e\u30bb\u30af\u30b7\u30e7\u30f3\u3067\u306f\u3001ActiveRecord\u306ejoin<\/code>\u30e1\u30bd\u30c3\u30c9\u306b\u3064\u3044\u3066\u3001\u57fa\u790e\u304b\u3089\u5fdc\u7528\u307e\u3067\u8a73\u3057\u304f\u898b\u3066\u3044\u304d\u307e\u3057\u3087\u3046\u3002<\/p>\n\n\n\nActiveRecord\u306ejoin\u30e1\u30bd\u30c3\u30c9\u3068\u306f\u4f55\u304b\uff1f\u521d\u5fc3\u8005\u306b\u3082\u308f\u304b\u308a\u3084\u3059\u304f\u89e3\u8aac<\/h3>\n\n\n\n
join<\/code>\u30e1\u30bd\u30c3\u30c9\u306f\u3001\u8907\u6570\u306e\u30c6\u30fc\u30d6\u30eb\u3092\u7d50\u5408\u3059\u308b\u305f\u3081\u306e\u30e1\u30bd\u30c3\u30c9\u3067\u3059\u3002
\u3053\u306e\u30e1\u30bd\u30c3\u30c9\u3092\u4f7f\u7528\u3059\u308b\u3068\u3001SQL\u306eJOIN\u53e5\u3092\u751f\u6210\u3057\u3001\u95a2\u9023\u4ed8\u3051\u3089\u308c\u305f\u30c6\u30fc\u30d6\u30eb\u9593\u3067\u30c7\u30fc\u30bf\u3092\u7d50\u5408\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002<\/p>\n\n\n\njoin<\/code>\u30e1\u30bd\u30c3\u30c9\u306e3\u3064\u306e\u4e3b\u306a\u7279\u5fb4<\/div>\n
join\u30e1\u30bd\u30c3\u30c9\u306e\u57fa\u672c\u7684\u306a\u69cb\u6587\u3068\u4f7f\u3044\u65b9\uff1a\u30b3\u30fc\u30c9\u4f8b\u3067\u5b66\u3076<\/h3>\n\n\n\n
join<\/code>\u30e1\u30bd\u30c3\u30c9\u306e\u57fa\u672c\u7684\u306a\u69cb\u6587\u306f\u975e\u5e38\u306b\u30b7\u30f3\u30d7\u30eb\u3067\u3059\u3002<\/p>\n\n\n\nModel.joins(:associated_model)<\/pre>\n\n\n\n
class User < ApplicationRecord\n has_many :posts\n has_many :comments\nend\n\nclass Post < ApplicationRecord\n belongs_to :user\n has_many :comments\nend\n\nclass Comment < ApplicationRecord\n belongs_to :user\n belongs_to :post\nend<\/pre>\n\n\n\n
\u5358\u4e00\u306e\u95a2\u9023\u4ed8\u3051\u3092\u4f7f\u7528\u3057\u305fjoin<\/h4>\n\n\n\n
# \u30e6\u30fc\u30b6\u30fc\u3068\u6295\u7a3f\u3092\u7d50\u5408\nusers_with_posts = User.joins(:posts)\n# \u751f\u6210\u3055\u308c\u308bSQL: SELECT users.* FROM users INNER JOIN posts ON posts.user_id = users.id<\/pre>\n\n\n\n
\u8907\u6570\u306e\u95a2\u9023\u4ed8\u3051\u3092\u4f7f\u7528\u3057\u305fjoin<\/h4>\n\n\n\n
# \u30e6\u30fc\u30b6\u30fc\u3068\u6295\u7a3f\u3068\u30b3\u30e1\u30f3\u30c8\u3092\u7d50\u5408\nusers_with_posts_and_comments = User.joins(:posts, :comments)\n# \u751f\u6210\u3055\u308c\u308bSQL: \n# SELECT users.* FROM users \n# INNER JOIN posts ON posts.user_id = users.id \n# INNER JOIN comments ON comments.user_id = users.id<\/pre>\n\n\n\n
\u30cd\u30b9\u30c8\u3055\u308c\u305f\u95a2\u9023\u4ed8\u3051\u3092\u4f7f\u7528\u3057\u305fjoin<\/h4>\n\n\n\n
# \u30e6\u30fc\u30b6\u30fc\u3068\u3001\u305d\u306e\u30e6\u30fc\u30b6\u30fc\u306e\u6295\u7a3f\u306b\u5bfe\u3059\u308b\u30b3\u30e1\u30f3\u30c8\u3092\u7d50\u5408\nusers_with_post_comments = User.joins(posts: :comments)\n# \u751f\u6210\u3055\u308c\u308bSQL:\n# SELECT users.* FROM users \n# INNER JOIN posts ON posts.user_id = users.id \n# INNER JOIN comments ON comments.post_id = posts.id<\/pre>\n\n\n\n
join<\/code>\u30e1\u30bd\u30c3\u30c9\u3092\u4f7f\u3046\u3053\u3068\u3067\u3001\u8907\u96d1\u306a\u95a2\u9023\u4ed8\u3051\u3082\u7c21\u5358\u306b\u8868\u73fe\u3067\u304d\u307e\u3059\u3002<\/p>\n\n\n\n# \u6761\u4ef6\u4ed8\u304djoin\nUser.joins(:posts).where(posts: { published: true })\n\n# \u30ab\u30b9\u30bf\u30e0SQL\u6587\u5b57\u5217\u3092\u4f7f\u7528\u3057\u305fjoin\nUser.joins(\"LEFT OUTER JOIN posts ON posts.user_id = users.id\")<\/pre>\n\n\n\njoin<\/code>\u30e1\u30bd\u30c3\u30c9\u306f\u975e\u5e38\u306b\u5f37\u529b\u3067\u3059\u304c\u3001\u4f7f\u7528\u3059\u308b\u969b\u306f\u3044\u304f\u3064\u304b\u306e\u6ce8\u610f\u70b9\u304c\u3042\u308a\u307e\u3059\u3002<\/p>\n\n\n\njoin<\/code>\u30e1\u30bd\u30c3\u30c9\u4f7f\u7528\u6642\u306e3\u3064\u306e\u6ce8\u610f\u70b9<\/div>\n
includes<\/code>\u30e1\u30bd\u30c3\u30c9\u3092\u4f7f\u7528\uff09<\/li>\n\n\n\njoin<\/code>\u30e1\u30bd\u30c3\u30c9\u3092\u4f7f\u3044\u3053\u306a\u3059\u3053\u3068\u3067\u3001\u52b9\u7387\u7684\u306a\u30af\u30a8\u30ea\u3092\u4f5c\u6210\u3057\u3001\u30a2\u30d7\u30ea\u30b1\u30fc\u30b7\u30e7\u30f3\u306e\u30d1\u30d5\u30a9\u30fc\u30de\u30f3\u30b9\u3092\u5411\u4e0a\u3055\u305b\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002
\u6b21\u306e\u30bb\u30af\u30b7\u30e7\u30f3\u3067\u306f\u3001\u3055\u307e\u3056\u307e\u306a\u30c7\u30fc\u30bf\u30d9\u30fc\u30b9\u7d50\u5408\u306e\u7a2e\u985e\u306b\u3064\u3044\u3066\u8a73\u3057\u304f\u898b\u3066\u3044\u304d\u307e\u3059\u3002<\/p>\n\n\n\n2. \u30c7\u30fc\u30bf\u30d9\u30fc\u30b9\u7d50\u5408\u306e\u7a2e\u985e\u3092\u5fb9\u5e95\u7406\u89e3<\/h2>\n\n\n\n
Ruby on Rails\u3067\u306f\u3001ActiveRecord\u3092\u901a\u3058\u3066\u69d8\u3005\u306a\u7a2e\u985e\u306e\u7d50\u5408\u3092\u7c21\u5358\u306b\u5b9f\u73fe\u3067\u304d\u307e\u3059\u3002
\u3053\u3053\u3067\u306f\u3001\u4e3b\u8981\u306a\u7d50\u5408\u306e\u7a2e\u985e\u3068\u305d\u306e\u7279\u5fb4\u3001\u305d\u3057\u3066Rails\u3067\u306e\u5b9f\u88c5\u65b9\u6cd5\u306b\u3064\u3044\u3066\u8a73\u3057\u304f\u898b\u3066\u3044\u304d\u307e\u3057\u3087\u3046\u3002<\/p>\n\n\n\nINNER JOIN\u3001LEFT OUTER JOIN\u3001RIGHT OUTER JOIN\u306e\u9055\u3044\u3068\u4f7f\u3044\u5206\u3051<\/h3>\n\n\n\n
\n
ruby User.joins(:posts) # SELECT users.* FROM users INNER JOIN posts ON posts.user_id = users.id<\/code><\/li>\n<\/ul>\n<\/div><\/div><\/div>\n\n\n\n\n
ruby User.left_outer_joins(:posts) # SELECT users.* FROM users LEFT OUTER JOIN posts ON posts.user_id = users.id<\/code><\/li>\n<\/ul>\n<\/div><\/div><\/div>\n\n\n\n\n
\u4f8b\u3048\u3070\u3001\u5168\u3066\u306e\u30e6\u30fc\u30b6\u30fc\u3068\u305d\u306e\u6295\u7a3f\uff08\u6295\u7a3f\u304c\u306a\u3044\u5834\u5408\u3082\u542b\u3080\uff09\u3092\u53d6\u5f97\u3057\u305f\u3044\u5834\u5408\u306f LEFT OUTER JOIN \u3092\u4f7f\u7528\u3057\u3001\u6295\u7a3f\u306e\u3042\u308b\u30e6\u30fc\u30b6\u30fc\u306e\u307f\u3092\u53d6\u5f97\u3057\u305f\u3044\u5834\u5408\u306f INNER JOIN \u3092\u4f7f\u7528\u3057\u307e\u3059\u3002<\/p>\n\n\n\n\u8907\u96d1\u306a\u7d50\u5408\u3092\u30b7\u30f3\u30d7\u30eb\u306b\u5b9f\u73fe\u3059\u308bRails\u306e\u30de\u30b8\u30c3\u30af<\/h3>\n\n\n\n
\u95a2\u9023\u4ed8\u3051\u3092\u5229\u7528\u3057\u305f\u81ea\u52d5\u7684\u306aJOIN\u751f\u6210<\/h4>\n\n\n\n
# \u6295\u7a3f\u3068\u305d\u306e\u30b3\u30e1\u30f3\u30c8\u3001\u3055\u3089\u306b\u30b3\u30e1\u30f3\u30c8\u3057\u305f\u30e6\u30fc\u30b6\u30fc\u3092\u7d50\u5408\n Post.joins(comments: :user)\n # SELECT posts.* FROM posts\n # INNER JOIN comments ON comments.post_id = posts.id\n # INNER JOIN users ON users.id = comments.user_id<\/pre>\n\n\n\n
\u30e1\u30bd\u30c3\u30c9\u30c1\u30a7\u30fc\u30f3\u306b\u3088\u308b\u8907\u96d1\u306a\u30af\u30a8\u30ea\u306e\u69cb\u7bc9
<\/h4>\n\n\n\n User.joins(:posts)\n .where(posts: { published: true })\n .where(\"posts.created_at > ?\", 1.week.ago)\n .select(\"users.*, COUNT(posts.id) as posts_count\")\n .group(\"users.id\")<\/pre>\n\n\n\nArel\u3092\u4f7f\u7528\u3057\u305f\u9ad8\u5ea6\u306a\u30af\u30a8\u30ea\u69cb\u7bc9
<\/h4>\n\n\n\n users = User.arel_table\n posts = Post.arel_table\n User.joins(users.join(posts, Arel::Nodes::OuterJoin)\n .on(users[:id].eq(posts[:user_id]))\n .join_sources)<\/pre>\n\n\n\n
joins<\/code>\u3068includes<\/code>\u306e\u9055\u3044\u306b\u3064\u3044\u3066\u6df1\u5800\u308a\u3057\u3001\u30d1\u30d5\u30a9\u30fc\u30de\u30f3\u30b9\u6700\u9069\u5316\u306e\u89b3\u70b9\u304b\u3089\u305d\u308c\u305e\u308c\u306e\u9069\u5207\u306a\u4f7f\u7528\u65b9\u6cd5\u3092\u898b\u3066\u3044\u304d\u307e\u3059\u3002<\/p>\n\n\n\n3. join\u3068includes\u306e\u9055\u3044\uff1a\u9069\u5207\u306a\u4f7f\u3044\u5206\u3051\u3067\u30d1\u30d5\u30a9\u30fc\u30de\u30f3\u30b9\u5411\u4e0a<\/h2>\n\n\n\n
joins<\/code>\u3068includes<\/code>\u30e1\u30bd\u30c3\u30c9\u306e\u9069\u5207\u306a\u4f7f\u3044\u5206\u3051\u304c\u91cd\u8981\u3067\u3059\u3002
\u3053\u308c\u3089\u306e\u30e1\u30bd\u30c3\u30c9\u306f\u4e00\u898b\u4f3c\u3066\u3044\u307e\u3059\u304c\u3001\u52d5\u4f5c\u3084\u7528\u9014\u306b\u5927\u304d\u306a\u9055\u3044\u304c\u3042\u308a\u307e\u3059\u3002
\u3053\u306e\u30bb\u30af\u30b7\u30e7\u30f3\u3067\u306f\u3001\u4e21\u8005\u306e\u9055\u3044\u3092\u7406\u89e3\u3057\u3001\u30d1\u30d5\u30a9\u30fc\u30de\u30f3\u30b9\u3092\u5411\u4e0a\u3055\u305b\u308b\u305f\u3081\u306e\u4f7f\u3044\u5206\u3051\u65b9\u3092\u5b66\u3073\u307e\u3057\u3087\u3046\u3002<\/p>\n\n\n\nN+1\u554f\u984c\u3092\u89e3\u6c7a\u3059\u308bincludes\u306e\u7279\u5fb4\u3068\u6d3b\u7528\u30b7\u30fc\u30f3<\/h3>\n\n\n\n
joins<\/code>\u3068includes<\/code>\u306e\u57fa\u672c\u7684\u306a\u9055\u3044\u3092\u7406\u89e3\u3059\u308b\u3053\u3068\u304b\u3089\u59cb\u3081\u307e\u3057\u3087\u3046\u3002<\/p>\n\n\n\njoin<\/code>\u30e1\u30bd\u30c3\u30c9<\/div><\/div>\n
includes<\/code>\u30e1\u30bd\u30c3\u30c9<\/div><\/div>\n
joins<\/code>\u3068\u6bd4\u3079\u3066\u591a\u304f\u306a\u308a\u307e\u3059\u3002<\/li>\n\n\n\nincludes<\/code>\u30e1\u30bd\u30c3\u30c9\u306e\u4e3b\u306a\u7279\u5fb4\u306f\u3001N+1\u554f\u984c\u3092\u89e3\u6c7a\u3067\u304d\u308b\u3053\u3068\u3067\u3059\u3002
N+1\u554f\u984c\u3068\u306f\u3001\u30c7\u30fc\u30bf\u30d9\u30fc\u30b9\u30af\u30a8\u30ea\u304c\u4e0d\u5fc5\u8981\u306b\u7e70\u308a\u8fd4\u3057\u5b9f\u884c\u3055\u308c\u308b\u554f\u984c\u306e\u3053\u3068\u3092\u6307\u3057\u307e\u3059\u3002
\u4f8b\u3048\u3070\u3001\u4ee5\u4e0b\u306e\u3088\u3046\u306a\u30b3\u30fc\u30c9\u3067N+1\u554f\u984c\u304c\u767a\u751f\u3057\u307e\u3059\u3002<\/p>\n\n\n\n# N+1\u554f\u984c\u304c\u767a\u751f\u3059\u308b\u30b3\u30fc\u30c9\nusers = User.all\nusers.each do |user|\n puts user.posts.count\nend<\/pre>\n\n\n\n
\u30e6\u30fc\u30b6\u30fc\u6570\u304c\u5897\u3048\u308b\u307b\u3069\u3001\u5b9f\u884c\u3055\u308c\u308b\u30af\u30a8\u30ea\u306e\u6570\u3082\u5897\u52a0\u3057\u3001\u30d1\u30d5\u30a9\u30fc\u30de\u30f3\u30b9\u304c\u4f4e\u4e0b\u3057\u307e\u3059\u3002<\/p>\n\n\n\nincludes<\/code>\u3092\u4f7f\u7528\u3059\u308b\u3053\u3068\u3067\u3001\u3053\u306e\u554f\u984c\u3092\u89e3\u6c7a\u3067\u304d\u307e\u3059\u3002<\/p>\n\n\n\n# includes\u3092\u4f7f\u7528\u3057\u3066N+1\u554f\u984c\u3092\u89e3\u6c7a\nusers = User.includes(:posts)\nusers.each do |user|\n puts user.posts.count\nend<\/pre>\n\n\n\n
\u3053\u308c\u306b\u3088\u308a\u3001\u30eb\u30fc\u30d7\u5185\u3067\u306e\u30c7\u30fc\u30bf\u30d9\u30fc\u30b9\u30a2\u30af\u30bb\u30b9\u304c\u4e0d\u8981\u306b\u306a\u308a\u3001\u30d1\u30d5\u30a9\u30fc\u30de\u30f3\u30b9\u304c\u5411\u4e0a\u3057\u307e\u3059\u3002<\/p>\n\n\n\njoin\u3068includes\u3092\u7d44\u307f\u5408\u308f\u305b\u305f\u6700\u9069\u306a\u30af\u30a8\u30ea\u8a2d\u8a08<\/h3>\n\n\n\n
joins<\/code>\u3068includes<\/code>\u306f\u3001\u305d\u308c\u305e\u308c\u4ee5\u4e0b\u306e\u3088\u3046\u306a\u5834\u9762\u3067\u4f7f\u7528\u3059\u308b\u3068\u52b9\u679c\u7684\u3067\u3059\u3002<\/p>\n\n\n\njoins<\/code>\u306e\u9069\u5207\u306a\u4f7f\u7528\u30b7\u30fc\u30f3<\/div><\/div>\n
includes<\/code>\u306e\u9069\u5207\u306a\u4f7f\u7528\u30b7\u30fc\u30f3<\/div><\/div>\n
joins<\/code>\u3068includes<\/code>\u3092\u7d44\u307f\u5408\u308f\u305b\u308b\u3053\u3068\u3067\u3001\u3055\u3089\u306b\u6700\u9069\u306a\u30af\u30a8\u30ea\u3092\u8a2d\u8a08\u3067\u304d\u307e\u3059\u3002
\u3053\u306e\u3068\u304d\u3001references<\/code>\u30e1\u30bd\u30c3\u30c9\u3092\u4f7f\u7528\u3057\u307e\u3059\uff1a<\/p>\n\n\n\n# joins\u3068includes\u3092\u7d44\u307f\u5408\u308f\u305b\u305f\u4f8b\nUser.includes(:posts).references(:posts).where(posts: { published: true })<\/pre>\n\n\n\n
\u3053\u308c\u306b\u3088\u308a\u3001\u30d5\u30a3\u30eb\u30bf\u30ea\u30f3\u30b0\u3068\u95a2\u9023\u30c7\u30fc\u30bf\u306e\u53d6\u5f97\u30921\u56de\u306e\u30af\u30a8\u30ea\u3067\u52b9\u7387\u7684\u306b\u884c\u3048\u307e\u3059\u3002<\/p>\n\n\n\njoins<\/code>\u3068includes<\/code>\u3092\u4f7f\u3044\u5206\u3051\u3001\u5fc5\u8981\u306b\u5fdc\u3058\u3066\u7d44\u307f\u5408\u308f\u305b\u308b\u3053\u3068\u3067\u3001\u30a2\u30d7\u30ea\u30b1\u30fc\u30b7\u30e7\u30f3\u306e\u30d1\u30d5\u30a9\u30fc\u30de\u30f3\u30b9\u3092\u5927\u5e45\u306b\u5411\u4e0a\u3055\u305b\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002
\u6b21\u306e\u30bb\u30af\u30b7\u30e7\u30f3\u3067\u306f\u3001\u3055\u3089\u306b\u8907\u96d1\u306a\u30c7\u30fc\u30bf\u69cb\u9020\u3067\u306ejoin<\/code>\u306e\u6d3b\u7528\u30c6\u30af\u30cb\u30c3\u30af\u306b\u3064\u3044\u3066\u6398\u308a\u4e0b\u3052\u3066\u3044\u304d\u307e\u3059\u3002<\/p>\n\n\n\n4. \u8907\u96d1\u306a\u30c7\u30fc\u30bf\u69cb\u9020\u3067\u306ejoin\u6d3b\u7528\u30c6\u30af\u30cb\u30c3\u30af<\/h2>\n\n\n\n
\u3053\u306e\u30bb\u30af\u30b7\u30e7\u30f3\u3067\u306f\u3001\u305d\u306e\u3088\u3046\u306a\u8907\u96d1\u306a\u30c7\u30fc\u30bf\u69cb\u9020\u306b\u5bfe\u3057\u3066join<\/code>\u3092\u52b9\u679c\u7684\u306b\u6d3b\u7528\u3059\u308b\u30c6\u30af\u30cb\u30c3\u30af\u3092\u7d39\u4ecb\u3057\u307e\u3059\u3002<\/p>\n\n\n\n\u591a\u5bfe\u591a\u95a2\u4fc2\u3092\u52b9\u7387\u7684\u306b\u6271\u3046join\u306e\u5fdc\u7528<\/h3>\n\n\n\n
\u4e00\u4eba\u306e\u30e6\u30fc\u30b6\u30fc\u304c\u8907\u6570\u306e\u6295\u7a3f\u3092\u6301\u3061\u3001\u5404\u6295\u7a3f\u306b\u8907\u6570\u306e\u30bf\u30b0\u304c\u4ed8\u3051\u3089\u308c\u308b\u5834\u5408\u3001\u3053\u308c\u306f\u591a\u5bfe\u591a\u95a2\u4fc2\u3068\u306a\u308a\u307e\u3059\u3002<\/p>\n\n\n\nhas_many :through<\/code>\u95a2\u9023\u4ed8\u3051\u3068join<\/code>\u30e1\u30bd\u30c3\u30c9\u3092\u7d44\u307f\u5408\u308f\u305b\u308b\u306e\u304c\u52b9\u679c\u7684\u3067\u3059\u3002
\u4ee5\u4e0b\u306b\u3001\u7279\u5b9a\u306e\u30bf\u30b0\u304c\u4ed8\u3044\u305f\u6295\u7a3f\u3092\u6301\u3064\u30e6\u30fc\u30b6\u30fc\u3092\u691c\u7d22\u3059\u308b\u4f8b\u3092\u793a\u3057\u307e\u3059\u3002<\/p>\n\n\n\nclass User < ApplicationRecord\n has_many :posts\n has_many :tags, through: :posts\nend\n\nclass Post < ApplicationRecord\n belongs_to :user\n has_many :taggings\n has_many :tags, through: :taggings\nend\n\nclass Tag < ApplicationRecord\n has_many :taggings\n has_many :posts, through: :taggings\nend\n\nclass Tagging < ApplicationRecord\n belongs_to :post\n belongs_to :tag\nend\n\n# \u7279\u5b9a\u306e\u30bf\u30b0\u304c\u4ed8\u3044\u305f\u6295\u7a3f\u3092\u6301\u3064\u30e6\u30fc\u30b6\u30fc\u3092\u691c\u7d22\nUser.joins(posts: :tags).where(tags: { name: 'Ruby' }).distinct<\/pre>\n\n\n\njoins<\/code>\u30e1\u30bd\u30c3\u30c9\u3092\u4f7f\u3063\u3066\u8907\u6570\u306e\u30c6\u30fc\u30d6\u30eb\u3092\u7d50\u5408\u3057\u3001where<\/code>\u30e1\u30bd\u30c3\u30c9\u3067\u6761\u4ef6\u3092\u6307\u5b9a\u3057\u3066\u3044\u307e\u3059\u3002distinct<\/code>\u30e1\u30bd\u30c3\u30c9\u3092\u4f7f\u7528\u3059\u308b\u3053\u3068\u3067\u3001\u91cd\u8907\u3059\u308b\u30e6\u30fc\u30b6\u30fc\u3092\u9664\u5916\u3057\u3066\u3044\u307e\u3059\u3002<\/p>\n\n\n\n\u30b5\u30d6\u30af\u30a8\u30ea\u3092\u4f7f\u3063\u305f\u9ad8\u5ea6\u306ajoin\u64cd\u4f5c\uff1a\u4e8b\u4f8b\u3068\u30b3\u30fc\u30c9\u89e3\u8aac<\/h3>\n\n\n\n
join<\/code>\u64cd\u4f5c\u304c\u6709\u52b9\u3067\u3059\u3002\u30b5\u30d6\u30af\u30a8\u30ea\u3068\u306f\u3001\u30e1\u30a4\u30f3\u30af\u30a8\u30ea\u306e\u4e2d\u306b\u57cb\u3081\u8fbc\u307e\u308c\u305f\u5225\u306e\u30af\u30a8\u30ea\u306e\u3053\u3068\u3067\u3001\u3053\u308c\u3092\u4f7f\u3046\u3053\u3068\u3067\u5358\u4e00\u306e\u30af\u30a8\u30ea\u3067\u3088\u308a\u8907\u96d1\u306a\u64cd\u4f5c\u3092\u5b9f\u73fe\u3067\u304d\u307e\u3059\u3002<\/p>\n\n\n\npopular_posts = Post.select('posts.user_id, COUNT(comments.id) AS comment_count')\n .joins(:comments)\n .where('comments.created_at > ?', 1.month.ago)\n .group('posts.user_id')\n .order('comment_count DESC')\n .limit(10)\n\nUser.joins(\"INNER JOIN (#{popular_posts.to_sql}) AS popular_posts ON users.id = popular_posts.user_id\")\n .select('users.*, popular_posts.comment_count')<\/pre>\n\n\n\npopular_posts<\/code>\u3068\u3044\u3046\u30b5\u30d6\u30af\u30a8\u30ea\u3092\u4f5c\u6210\u3057\u3001\u305d\u308c\u3092\u30e1\u30a4\u30f3\u306e\u30e6\u30fc\u30b6\u30fc\u30af\u30a8\u30ea\u306bjoin<\/code>\u3057\u3066\u3044\u307e\u3059\u3002to_sql<\/code>\u30e1\u30bd\u30c3\u30c9\u3092\u4f7f\u7528\u3057\u3066\u30b5\u30d6\u30af\u30a8\u30ea\u3092SQL\u6587\u5b57\u5217\u306b\u5909\u63db\u3059\u308b\u3053\u3068\u3067\u3001\u8907\u96d1\u306a\u6761\u4ef6\u3092\u5358\u4e00\u306e\u30af\u30a8\u30ea\u3067\u8868\u73fe\u3057\u3066\u3044\u307e\u3059\u3002<\/p>\n\n\n\njoin<\/code>\u30af\u30a8\u30ea\u3092\u69cb\u7bc9\u3059\u308b\u969b\u306f\u3001\u4ee5\u4e0b\u306e\u624b\u9806\u3092\u610f\u8b58\u3059\u308b\u3068\u826f\u3044\u3067\u3057\u3087\u3046\u3002<\/p>\n\n\n\njoin<\/code>\u30e1\u30bd\u30c3\u30c9\u5229\u7528\u6642\u306b\u610f\u8b58\u3059\u3079\u304d\u624b\u9806\u30105STEP\u3011<\/div>\n
join<\/code>\u30e1\u30bd\u30c3\u30c9\u3092\u4f7f\u7528\u3057\u3066\u57fa\u672c\u7684\u306a\u7d50\u5408\u3092\u884c\u3046<\/li>\n\n\n\nwhere<\/code>\u30e1\u30bd\u30c3\u30c9\u3067\u7d5e\u308a\u8fbc\u307f\u6761\u4ef6\u3092\u8ffd\u52a0\u3059\u308b<\/li>\n\n\n\nselect<\/code>\u30e1\u30bd\u30c3\u30c9\u3067\u53d6\u5f97\u3059\u308b\u30ab\u30e9\u30e0\u3092\u6307\u5b9a\u3059\u308b<\/li>\n\n\n\norder<\/code>\u30e1\u30bd\u30c3\u30c9\u3067\u4e26\u3073\u66ff\u3048\u3092\u884c\u3046<\/li>\n<\/ol>\n<\/div><\/div>\n\n\n\n\u30d1\u30d5\u30a9\u30fc\u30de\u30f3\u30b9\u3068\u53ef\u8aad\u6027\u306e\u30d0\u30e9\u30f3\u30b9\u3092\u8003\u616e\u3057\u305f\u30d9\u30b9\u30c8\u30d7\u30e9\u30af\u30c6\u30a3\u30b9<\/h3>\n\n\n\n
join<\/code>\u64cd\u4f5c\u3092\u884c\u3046\u969b\u306f\u3001\u30d1\u30d5\u30a9\u30fc\u30de\u30f3\u30b9\u3068\u53ef\u8aad\u6027\u306e\u30d0\u30e9\u30f3\u30b9\u3092\u53d6\u308b\u3053\u3068\u304c\u91cd\u8981\u3067\u3059\u3002\u4ee5\u4e0b\u306b\u3044\u304f\u3064\u304b\u306e\u30d9\u30b9\u30c8\u30d7\u30e9\u30af\u30c6\u30a3\u30b9\u3092\u7d39\u4ecb\u3057\u307e\u3059\u3002<\/p>\n\n\n\n\u30a4\u30f3\u30c7\u30c3\u30af\u30b9\u306e\u9069\u5207\u306a\u8a2d\u5b9a<\/h4>\n\n\n\n
\u5fc5\u8981\u6700\u5c0f\u9650\u306e\u30c7\u30fc\u30bf\u53d6\u5f97<\/h4>\n\n\n\n
select<\/code>\u30e1\u30bd\u30c3\u30c9\u3092\u4f7f\u7528\u3057\u3066\u3001\u5fc5\u8981\u306a\u30ab\u30e9\u30e0\u306e\u307f\u3092\u53d6\u5f97\u3059\u308b\u3088\u3046\u306b\u3057\u307e\u3059\u3002<\/p>\n\n\n\n User.joins(:posts).select('users.id, users.name, COUNT(posts.id) AS post_count')<\/pre>\n\n\n\n\u30af\u30a8\u30ea\u306e\u30e2\u30b8\u30e5\u30fc\u30eb\u5316<\/h4>\n\n\n\n