mysql - Rails:如何通过两个不同的关系加入两个模型？

我有两种模式：Saft（杂志）和Keyword。每个“ Saft”均由一系列关键字定义，但也具有标题，该标题始终是其关键字之一。 Saft和Keyword模型通过HABTM联接表连接，以提取所有关键字，现在我也尝试将标题从关键字表提取到saft / show.html.erb上。我试图使用class_name选项以拉标题。因此，我创建了Edition模型。

class Saft < ActiveRecord::Base
#  attr_accessible :colour, :cover_alt, :description, :number, :short
  has_and_belongs_to_many :keywords, :join_table => "safts_keywords"
  has_one :title, :through => :edition, :class_name => "keyword"
  has_one :edition
end

class Keyword < ActiveRecord::Base
#  attr_accessible :word, :description
  has_and_belongs_to_many :safts, :join_table => "safts_keywords"
  belongs_to :issue, :through => :edition, :class_name => "saft"
  belongs_to :edition
end

class Edition < ActiveRecord::Base
#  attr_accessible :saft_id, :keyword_id
  belongs_to :title
  belongs_to :issue
end

class SaftsController < ApplicationController
  def show
    @saft = Saft.find(params[:id])
  end

show.html.erb
    <%= @saft.title.upcase %>

我收到以下错误：

Started GET "/safts/2" for 127.0.0.1 at Sat Feb 10 17:31:28 +0100 2018
Connecting to database specified by database.yml
Processing by SaftsController#show as HTML
  Parameters: {"id"=>"2"}
  Saft Load (1.8ms)  SELECT `safts`.* FROM `safts` WHERE `safts`.`id` = ? LIMIT 1  [["id", "2"]]
  Image Load (0.3ms)  SELECT `images`.* FROM `images` WHERE `images`.`saft_id` = 2
  Rendered safts/show.html.erb within layouts/public (35.0ms)
Completed 500 Internal Server Error in 103ms

ActionView::Template::Error (uninitialized constant Saft::keyword):
    29:                 </div>
    30:                 <div class="saft_box col-content">
    31:                     <div class="saft_keyword">
    32:                         <strong><%= @saft.title.upcase %></strong>
    33:                     </div>
    34:                     <div class="saft_description">
    35:                         <p><%= @saft.description %></p>
  app/views/safts/show.html.erb:32:in `_app_views_safts_show_html_erb___758994895_2167416580'

我该如何工作？

取消注释@ saft.title.upcase时，此实现还会破坏Saft关键字关联，我通过取消注释关键字模型中的belongs_to：issue部分来重新进行工作。

最佳答案

您的模型有一些变化：

class Saft < ActiveRecord::Base
  #You don't need attr_accessible for fields in safts table
  has_and_belongs_to_many :keywords, :join_table => "safts_keywords"

  #The specific keyword that acts as title.
  #You need a new field in safts table named title_id which references to a Keyword.
  belongs_to :title, class_name => "Keyword", :foreign_key => 'title_id'
end

class Keyword < ActiveRecord::Base
  #You don't need attr_accessible for fields in keywords table
  has_and_belongs_to_many :safts, :join_table => "safts_keywords"
end

要获取Saft标题，请使用@saft.title.word.upcase if @saft.title

对于您的OP中的用例，我认为您不需要模型上的任何其他内容。