在与Rails深度嵌套的关联中查找记录 [英] Find records in deeply nested associations with rails

问题描述

我有以下型号:

class Book < ApplicationRecord
  has_many :chapters
end

class Chapter < ApplicationRecord
  belongs_to :book
  has_many :pages
end

class Page < ApplicationRecord
  belongs_to :chapter
  has_many :paragraphs
end

class Paragrpah < ApplicationRecord
  belongs_to :page
end

现在，我想获取一本特定书籍中所有段落的列表.像这样:

Now I want to get a list of all paragraphs in a specific book. Something like:

@parapgraphs = Paragraph.pages.chapters.book.where(:title => 'My Book')

这样做，我得到:

undefined method 'chapters' for 'pages'

我正在使用Rails 4.2和Ruby 2.2

I'm using Rails 4.2 and Ruby 2.2

推荐答案

如果您希望这些对象之间的链接始终存在并且可查询，请考虑通过关系添加has_many.

If you want links between any of those objects to always be present and queryable, consider adding a has_many through relationship.

http://guides.rubyonrails.org/association_basics.html#the-has-many-through-association

如果是一次查询，则可以执行以下操作

If it's more of a one time query, you could do something like this

@paragraphs = Paragraph.joins(page: { chapter: :book }).where(books: { title: 'My Book' })

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