如何手动构建一个正确的嵌套表单,它接受嵌套的属性?

我正在尝试为测试目的手动构建表单字段。我有以下型号:

class Bedroom < ActiveRecord::Base
    has_many :booked_bedrooms
    has_many :bookings, :through => :booked_bedrooms
end

class Booking < ActiveRecord::Base
    has_many :booked_bedrooms
    has_many :bedrooms, :through => :booked_bedrooms
    accepts_nested_attributes_for :booked_bedrooms
end

class BookedBedroom < ActiveRecord::Base
    belongs_to :booking
    belongs_to :bedroom
    # fields: bedroom_id, :booking_id
end

当我在控制台中尝试以下操作时,将保存预订和关联的预订房间:

>> b = Booking.new({ :booked_bedrooms_attributes => { 0 => { :bedroom_id => 1  }  }  })
=> #<Booking id: nil, start_date: nil, end_date: nil, created_at: nil, updated_at: nil>
>> b.save
=> true
>> b.booked_bedrooms
=> [#<BookedBedroom id: 1, booking_id: 1, bedroom_id: 1, created_at: "2010-06-22 18:55:57", updated_at: "2010-06-22 18:55:57">]

所以我建了一个这样的模型:

<% form_for @booking do |form| %>
<% for bedroom in @available_bedrooms %>

            <%= check_box_tag "booked_bedrooms_attributes[#{bedroom.id}][bedroom_id]", bedroom.id %> <%= bedroom.name %>  
            as
            <%= select_tag "booked_bedrooms_attributes[#{bedroom.id}][booking_type_id]", options_for_select(bedroom.booking_types.map {|p| [p.name, p.id]}) %>
<% end %>
<% end %>

我知道我可以使用formtastic或一些字段,但我想以硬编码的形式解决这个问题,以便于演示。