Ruby on Rails 3 - has_many ：通过不从<class>基地访问_id

Question

型号代码

class Location < ActiveRecord::Base
  attr_accessible :day_tokens, :name, :address, :phone
  has_many :locavailability
  has_many  :dayavailables, :through => :locavailability
  attr_reader :day_tokens
  def day_tokens=(ids)
    self.locavailability.dayavailable_id= ids.split(",")
  end
end
class Dayavailable < ActiveRecord::Base
  has_many  :locavailability
  has_many  :locations, :through => :locavailability
end
class Locavailability < ActiveRecord::Base
  attr_accessible :dayavailable_id, :location_id
  belongs_to :dayavailable
  belongs_to :location
end

数据库列：

locations: id, name, address, phone, hours, created_at, updated_at
dayavailables: id, day, time, created_at, updated_at
locavailabilities: id, location_id, dayavailable_id, created_at, updated_at

错误

irb(main):004:0> l = Location.find(1)
=> #<Location id: 1, name: "test", address: "123 Fake Street", phone: "23443234324", hours: "M-F 9 - 5", created_at: "2011-05-16 04:56:31", updated_at: "2011-05-16 04:56:31">
irb(main):005:0> l.class
=> Location(id: integer, name: string, address: string, phone: string, hours: string, dentistry_id: integer, created_at: datetime, updated_at: datetime)
irb(main):006:0> l.locavailability
=> []
irb(main):007:0> l.dayavailable_id
NoMethodError: undefined method `dayavailable_id' for #<Location:0xb6af7c40>
    from /usr/lib/ruby/gems/1.8/gems/activemodel-3.0.0/lib/active_model/attribute_methods.rb:364:in `method_missing'
    from /usr/lib/ruby/gems/1.8/gems/activerecord-3.0.0/lib/active_record/attribute_methods.rb:46:in `method_missing'
    from /usr/lib/ruby/gems/1.8/gems/activerecord-3.0.0/lib/active_record/attribute_methods.rb:44:in `send'
    from /usr/lib/ruby/gems/1.8/gems/activerecord-3.0.0/lib/active_record/attribute_methods.rb:44:in `method_missing'
    from (irb):6

Location类不应该访问dayavailable_id吗？？我正在按照github 上railscasts第258集的代码进行

我错过了什么？

Answer 1

为什么Location应该访问dayavailable_id？如果给定true，则dayavailable_id是locavailabilities的列：

数据库列：

位置：id，名称，地址，电话，小时，created_at，updated_at

可用日期：id，day，time，created_at，updated_at

本地可用性：id，location_id，dayavailable_id，created_at，updated_at

试试这个：更新

l = Location.find(1)
l.dayavailable_ids #=> Returns an array of the associated objects’ ids

但如果调用dayavailable_id，它应该是表的一列。

因此l.dayavailable_ids将执行此DB查询：

select id from dayavailables d
inner join locavailabilities l on l.dayavailable_id = d.id 
where l.location_id = 1 

但是Locability.find（1）.dayavailable_id将执行这个DB查询（不是真的，只是为了更可读）：

select dayavailable_id from locavailabilities l
where l.location_id = 1