ruby-on-rails-3 - 导轨 : ActiveRecord Query for has_many :through model

Question

如何查询具有“has_many :through”关系的某个分支的公司？

  #company.rb
  has_many :branch_choices
  has_many :branches, :through => :branch_choices

“查找所有分支机构 ID 为 3 的公司”

Answer 1

Company.includes(:branches).where(:branches => {:id => 3})

或者

Branch.find(3).companies

更新
实际上，第一个代码段有一个缺点:它急切地将分支机构与公司一起加载。为了避免这种开销，您可以考虑使用左连接:

Company.
  joins("LEFT JOIN `branch_choices` ON `branch_choices`.`company_id` = `companies`.`id`").
  where(:branch_choices => {:branch_id => 3})