Rails过滤多对多关系中的记录 [英] Rails filtering records in many to many relationship

问题描述

我与书籍和作者之间有很多联系，例如：

I have many to many relationship for books and authors like:

class Book < ApplicationRecord
  has_many :books_authors, inverse_of: :author, dependent: :destroy
  has_many :authors, through: :books_authors
end

class Author < ApplicationRecord
  has_many :books_authors, dependent: :destroy
  has_many :books, through: :books_authors
end

class AuthorsBook < ApplicationRecord
  belongs_to :author
  belongs_to :book
end

现在获取所有图书，其中个作者的 id：1和3
查询类似于：

Now to get all the Books with Authors of ids: 1 and 3 The query is like :

Book.joins(:authors).where(authors: {id:  [1, 3]}).uniq

Book.joins(:books_authors).where(books_authors: {author_id:  [1,3]}).uniq

Book.joins(:authors).where('authors.id IN (?)', [1,3]).uniq 

但是我得到一本书的作者ID为 2,3,5 ，但事实并非如此，因为它没有 author id 1 。

But I get a book whose authors' ids are 2,3,5, which should not be the case, as it does not have author with id 1.

所以，我怎么能具有给定作者ID的书？

So , how could I only get the books with given authors ids?

推荐答案

您需要具有子句在那里结合您的where子句：

You need a having clause in there combined with your where clause:

ids = [1,3]
Book
  .select('books.*') # not sure if this is necessary
  .where(authors_books: { author_id: ids })
  .joins(:authors_books)
  .group('books.id')
  .having('count(authors_books) >= ?', ids.size)

SQL： https://www.db-fiddle.com/f/i7TXPJgavLwQCHb4GhgH3b/0

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