ActiveRecordのmergeについて

クエリの結合ができるメソッド

クエリの結合

code: (rb)

# mergeを使わない

Book.where(title: 'タイトル', author: 'Alice')

# mergeでクエリ結合

title_query = Book.where(title: 'タイトル')

author_query = Book.where(author: 'Alice')

title_query.merge(author_query)

# 1行でクエリ結合

Book.where(title: 'タイトル').merge(Book.where(author: 'Alice'))

code: (sql)

SELECT books.* FROM books WHERE title = 'タイトル' AND author = 'Alice';

スコープの結合

code: (rb)

class User < ApplicationRecord

has_many :books

end

class Book < ApplicationRecord

belongs_to :user

scope :published, -> { where(is_published: true) }

end

code: (rb)

published_books = Book.published

User.joins(:books).merge(published_books)

# 1行

User.joins(:books).merge(Book.published)

code: (sql)

SELECT

users.*

FROM

users

INNER JOIN

books

ON

books.user_id = users.id

WHERE

books.is_published = TRUE

;

参照