在Rails的ActiveRecord，加入與has_and_belongs_to_many在命名空間模型

Question

我有一個命名空間中兩種型號，服務和教練，這兩者有許多相互一對多的關係，通過has_and_belongs_to_many定義不起作用：

class Scheduling::Service < ActiveRecord::Base 

    has_and_belongs_to_many :instructors 
end 

class Scheduling::Instructor < ActiveRecord::Base 
    attr_accessible :first_name, :last_name 
    has_many :instructor_availabilities 

    scope :of_service, lambda { |service_id| joins(:services).where(:services => {:id => service_id})} 

    has_and_belongs_to_many :services, :class_name => "Scheduling::Service" 
end 

在_service的範圍中，我希望of_service返回與服務關聯的所有教師。

但是，運行這個範圍時，我得到一個錯誤：

ActiveRecord::StatementInvalid: PG::Error: ERROR: missing FROM-clause entry for table "services" LINE 1: ...."id" = "instructors_services"."service_id" WHERE "services"... ^ : SELECT "scheduling_instructors".* FROM "scheduling_instructors" INNER JOIN "instructors_services" ON "instructors_services"."instructor_id" = "scheduling_instructors"."id" INNER JOIN "scheduling_services" ON "scheduling_services"."id" = "instructors_services"."service_id" WHERE "services"."id" = 107 LIMIT 1

它似乎是想錯了的是，其加入的表稱爲instructors_services（該表犯規存在），忽略了命名空間相關模型。它應該加入名爲scheduling_instructors_services的表，該表與名稱空間一致。

Answer 1

嘗試增加:join_table => 'scheduling_instructors_services'你的關係是這樣的：

has_and_belongs_to_many :instructors, :class_name => "Scheduling::Instructor", :join_table => 'scheduling_instructors_services' 
has_and_belongs_to_many :services, :class_name => "Scheduling:: Service", :join_table => 'scheduling_instructors_services' 

而且，應該不會是

.where('instructors_services.id' => service_id)

，而不是

.where(:services => {:id => service_id})