ruby-on-rails - 在rails 3中查询相关的has_many模型

Question

我有两个模型User和Service。Userhas_and_belongs_to_manyServices同样适用于Services：

class User < ActiveRecord::Base
  has_and_belongs_to_many :services
end

class Service < ActiveRecord::Base
  has_and_belongs_to_many :users
end

我需要找到所有提供选定服务的用户。就像是：

@users = User.where(:services_ids => [2,3,4])

Answer 1

这应该有效：

User.join(:services).where(:services.id => [2,3,4]).uniq

Answer 2

尝试这个：

@users = Service.where(:id => [2,3,4])).map{|svc| svc.users}.uniq.flatten

或者

@users = User.all(:include => :services, :conditions => ["services.id in ?", (2,3,4)])