mysql - rails : how to join two models through two different relations?

Question

我有两个模型:Saft(杂志)和 Keyword。每个“Saft”都由一系列关键字定义，但也有一个标题，该标题始终是其关键字之一。 Saft 和关键字模型通过 HABTM 连接表连接，以便提取所有关键字，现在我也尝试将标题从关键字表提取到 saft/show.html.erb 上。我正在尝试使用 class_name 选项来提取标题。因此我创建了版本模型。

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'

我怎样才能让它工作？

当取消注释@saft.title.upcase时，此实现也会破坏Saft关键字关联，我通过取消注释关键字模型中的belongs_to :issue部分来再次工作。

Answer 1

模型中的一些更改:

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

我认为对于 OP 中的用例，您的模型不需要任何其他内容。