Question

我发现了一些关于STI的好信息，但没有看到我想做的事情的例子。这是我能想到的最好的例子。我希望能够跟踪两个实体，但它们不需要自己的表。我只需要区分类型（STI可以做到这一点），但我还需要知道一个实体是否以及如何与另一个实体相关。我会以书籍为例。有些书只是书本，但其他实体书籍是多本书的集合。

表：书籍

id | title | author_id | book_id
1, 'Fellowship of the Ring, 34, (NULL)      # is a physical book
2, 'The Two Towers', 34, (NULL)             # is a physical book
3, 'American Gods', 1, (NULL)               # is a physical book
4, 'Complete Lord Of the Rings', 34, (NULL)
5, 'Fellowship of the Ring', 34, 4          # is collected within book id 4
6, 'The Two Towers', 34, 4                  # is also collected within book id 4
etc.

所以我希望能够查询书籍，查阅所有书籍，并通过'book_id'了解它们是如何以及是否相互关联

这在Rails中可行吗？如果是这样，它如何最好地实施？我可以在书籍模型中说'has_many：books'吗？他们的陷阱或担忧等等？

提前谢谢。

Answer 1

这样的事情可能对你的情况有用吗？

class Book < ActiveRecord::Base
  # all attributes of a book
end

class SeriesBook < Book
  has_many :books, :class_name => "PhysicalBook", :foreign_key => "parent_id"
end

class PhysicalBook < Book
  belongs_to :series, :class_name => "SeriesBook", :foreign_key => "parent_id"
end

然后查询时

# searches both Series and Physical
Book.where("title LIKE ?", "#{params[:title]}%") 
# searches only Series
SeriesBook.where("title LIKE ?", "#{params[:title]}%")

你可能会发现你真的希望你的模特与众不同吗？系列和书籍而不使用STI？它会使两者之间的查询更复杂，但可能会使应用程序的其余部分更容易理解

更新：将belongs_to添加到PhysicalBook，has_many关联上的类名

# How would I query a specific collection to see which and how many books it has within it?
series = SeriesBook.find(0000)
series.books.length # => how many 
series.books.each do |book|
  puts book.title
end

# How would I look at a book and see if it was in a collection and, 
# if so, the specific ID of the specific collection to which it is associated
book = PhysicalBook.find(0000)
puts book.series.title
puts book.series.id

书籍数据库表最终看起来像

id # primary key
title
# other book columns ....
type # STI
parent_id # nullable, used by physical book when part of a series, points to books.id on the series book

另外：请阅读 - http://rhnh.net/2010/07/02/3-reasons-why-you-should-not-use-single-table-inheritance

你可能不想要STI吗？数据模型看起来与上面类似，但没有STI，即Series / Book

在has_many和belongs_to中使用foreign_key可能会令人困惑：请在此处阅读 - http://guides.rubyonrails.org/association_basics.html

具有关系的单表继承？

1 个答案: