Question

我正在尝试使用包含对自身引用的连接表为模型构建表单。我会给你一个快速的例子，说明我想要实现的目标：

让我说我有主题物理。要学习物理，你需要知道基础数学，即物理学依赖于数学。任何主题都应该能够兼有多种依赖关系。我遇到的问题是通过表格提交这种关系。

我的代码：

型号：

class Subject < ActiveRecord::Base
    has_many :needs, foreign_key: :target_id
    has_many :subjects, through: :needs

    accepts_nested_attributes_for :needs,:subjects,allow_destroy: true
end
class Need < ActiveRecord::Base
    belongs_to :target, class_name: :subject
    belongs_to :prerequisite, class_name: :subject
end

控制器：

class SubjectsController < ApplicationController
def create
  @subject = Subject.new secure_params
  if @subject.save
    redirect_to root_path, success: 'Subject created'
  else
    render :new
  end
end

def new
  @subject = Subject.new
end

private

def secure_params
  params.require(:subject).permit(:name, :content, needs_attributes: [:target,:prerequisite])
  end
end

表格：

<div class="row">
 <div class="col-md-8">
   <%= simple_nested_form_for @subject do |f| %>
       <%= f.input :name %>
       <%= f.input :content %>

       <%= f.fields_for :needs do |d| %>
           <%=d.association :prerequisite %>
       <% end %>
       <%= f.link_to_add "Add a prerequisite", :needs %>

       <%= f.submit class: 'btn btn-primary btn-lg' %>
   <% end %>
 </div>
</div>

使用这种方法，我在进入“新”动作时得到“未初始化的常量Need :: subject”。任何关于我的方法或代码中的错误的想法将不胜感激。编辑：添加连接表

class CreateNeeds < ActiveRecord::Migration
  def change
    create_table :needs do |t|

      t.references :target
      t.references :prerequisite
    end
  end
end

Edit2：工作代码（仅更改了部分）

模型

 class Subject < ActiveRecord::Base
    has_many :needs, foreign_key: :target_id
    has_many :prerequisites, class_name: "Subject",through: :needs, source: :prerequisites

    accepts_nested_attributes_for :needs,:prerequisites,allow_destroy: true
end
class Need < ActiveRecord::Base
    belongs_to :target, class_name: "Subject"
    belongs_to :prerequisite, class_name: "Subject"
end

控制器

   def secure_params
  params.require(:subject).permit(:name, :content, needs_attributes: [:prerequisite_id])
  end
end

Answer 1

就像我在评论中所说的那样，在你担心表格之前，要注意确保所有关联都正确连接。控制台或自动化测试都是测试它的好地方。

我认为应该是这样的：

class Subject < ActiveRecord::Base
  has_many :needs,  as: :target
  has_many :subjects, :class_name: "Subject",  through: :needs, source: :prerequisite

  accepts_nested_attributes_for :needs,:subjects,allow_destroy: true
end

#assuming you have fields target_id and prerequisite_id in this table
class Need < ActiveRecord::Base
  belongs_to :target, class_name: :subject
  belongs_to :prerequisite, class_name: :subject
end

我认为协会名称＆＃34;科目＆＃34;可能会引起混淆，因为它会返回此主题所需的主题。这对读者来说并不是显而易见的，将来可能包括你。

在某些时候，您可能希望列出需要此主题的主题。现在可能值得区分这些，所以你可以清楚地区分它们。你可以这样做：

class Subject < ActiveRecord::Base
  has_many :required_needs,  as: :target
  has_many :required_by_needs,  as: :prerequisite

  has_many :required_subjects, :class_name: "Subject",  through: :required_needs, source: :prerequisite
  has_many :required_by_subjects, :class_name: "Subject",  through: :required_by_needs, source: :target

  accepts_nested_attributes_for :required_needs, :required_by_needs, :required_subjects, :required_by_subjects, allow_destroy: true
end

Rails：根据自己的模型为连接表创建表单字段

1 个答案: