如何管理3多到很多车型在Rails中 [英] how to manage 3 many-to-many models in Rails

问题描述

我下面做一个不同型号的 Railscast 咨询维持多到许多的关系。但是，我无法提取传递关系数据。

想象一下，有3个型号，多到很多：用户＆LT; - ＆GT;颜色和LT; - ＆GT;百叶窗

我做了2个型号：

Col​​orLiking（保持用户的LT; - ＆GT;颜色），DiffShades（保持颜色＆LT; - ＆GT;百叶窗）

问题 现在，如果一切设置正确......我怎么找到百叶窗是属于用户？

我将如何建立这种关系？

 类用户的LT;的ActiveRecord :: Base的
   的has_many：色调，：通过=＆GT;：diffShades，：源=＆GT; ：颜色
结束
 

上面似乎没有工作...

使用SQL下面的查询将工作：

  SELECT * FROM色调
  其中id在（选择diffshades shade_id
                其中，COLOR_ID中（从colorlikings选择COLOR_ID
                                     其中，USER_ID =？））
 

解决方案

这是空中code，它至少部分地错了，但也许有用把你一个高效的轨道上调查

长话短说是的ActiveRecord不会得到你一路到User.shades方法只瓦特/不同：有和：属于调用。但是，这不是太可怕写你自己的模型方法来做到这一点。

 类用户的LT;的ActiveRecord :: Base的
   的has_many：color_likings
   的has_many：颜色，：通过=＆GT; ：color_likings

   高清get_shades
     colors.collect {| C | c.shades.to_a} .flatten
   结束
结束

类ColorLiking＆LT;的ActiveRecord :: Base的
  belongs_to的：用户
  belongs_to的：颜色
结束

一流的颜色
  的has_many：color_likings
  的has_many：用户：通过=＆GT; ：color_likings
结束

类DiffShade
  belongs_to的：颜色
  belongs_to的：灯罩
结束

一流的阴影
  的has_many：diff_shades
  的has_many：颜色，：通过=＆GT; ：diff_shades
结束
 

I'm following Railscast Advice of making a different model to maintain many-to-many relationships. However, I am having trouble extracting transitive relation data.

Imagine that there are 3 models with many-to-many: User <-> Color <-> Shades

I've made 2 more models:

ColorLiking (maintains User <-> Color), DiffShades (maintains Color <-> Shades)

Question Now, If everything is set up correctly...how do I find the Shades that belong to a User?

How Will I setup that relationship?

class User < ActiveRecord::Base
   has_many :shades, :through=>:diffShades, :source => :color
end

above does not seem to work...

Using SQL the below query would work:

select * from shades 
  where id in (select shade_id from diffshades 
                where color_id in (select color_id from colorlikings 
                                     where user_id = ?))

解决方案

This is air code and probably at least partially wrong, but maybe useful to put you on a productive track investigating.

Long story short is that ActiveRecord won't get you all the way to a User.shades method just w/the various :has and :belongs calls. But it's not too terrible to write your own model method to do it.

class User < ActiveRecord::Base
   has_many :color_likings
   has_many :colors, :through => :color_likings

   def get_shades
     colors.collect {|c| c.shades.to_a}.flatten
   end
end

class ColorLiking < ActiveRecord::Base
  belongs_to :user
  belongs_to :color
end

class Color
  has_many :color_likings
  has_many :users, :through => :color_likings  
end

class DiffShade
  belongs_to :color
  belongs_to :shade
end

class Shade
  has_many :diff_shades
  has_many :colors, :through => :diff_shades
end

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