查詢有關has_many模型的rails 3

Question

我有兩種模式User和Service。 User has_and_belongs_to_many Services同樣適用於Services：

class User < ActiveRecord::Base 
    has_and_belongs_to_many :services 
end 

class Service < ActiveRecord::Base 
    has_and_belongs_to_many :users 
end 

我需要找到誰提供特定服務的所有用戶。喜歡的東西：

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

Answer 1

試試這個：

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

或

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

Answer 2

這應該工作：

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