ruby-on-rails - 通过Ruby on Rails中的联接表选择记录

Question

我有三种模式

class Collection < ActiveRecord::Base
  has_many :presentations
  has_many :galleries, :through => :presentations
end

class Gallery < ActiveRecord::Base    
  has_many :presentations
  has_many :collections, :through => :presentations
end

class Presentation < ActiveRecord::Base
  belongs_to :collection
  belongs_to :gallery 
end

如何获得不属于给定画廊的所有收藏？

我的SQL知识只是基本知识。我也想让Rails（2.3）完成工作而无需显式使用SQL表达式。

Answer 1

开箱即用，从技术上讲，您必须编写一些SQL（where子句）...

gallery_to_exclude = Gallery.first
Collection.find(:all,
  :include => :presentations,
  :conditions => ['presentations.gallery_id IS NULL OR presentations.gallery_id != ?',
                   gallery_to_exclude.id])

但是，如果要使用 Searchlogic，可以避免这种情况：

Collection.presentations_gallery_id_is_not(gallery_to_exclude.id).all