如何从一种形式使用 fields_for 到 link 多个模型？

Question

我正在构建一个注册应用程序。共有三种模型：Participant、Volunteer_Detail 和Student_Detail。 Participant has_one 其他两个模型，而他们依次 belongs_to Participant。我正在尝试使用一种带有 fields_for 的表格向 Participant 和其他模型之一提供数据。

我一直收到错误消息，说用于 Student_Detail 的属性之一不是 Participant 的已定义属性。

我查看了 fields_for 上的几个指南，似乎有几种方法可以定义您的表单适用的第二个模型。

共识似乎应该是这样的：

         <%= f.fields_for @participant.student_details do |student_detail_field| %>
                    <%= f.label :nationality, 'Nationality:' %> 
                    <%= student_detail_field.text_field :nationality %>

然而，当我写 :student_details 而不是 @participant.student_details.

时，它似乎只显示我的表格

这是我的表格，显示了顶部部分，以及包含 fields_for 的部分（表格被修剪以保存 space）：

                    <%= f.label :first_name, 'First:' %>
                    <%= f.text_field :first_name %>

         <%= f.fields_for :student_details do |student_detail_field| %>
                    <%= f.label :nationality, 'Nationality:' %> 
                    <%= student_detail_field.text_field :nationality %>

这是我的参与者控制器：

class ParticipantsController < ApplicationController 定义新 @参与者= Participant.new 结束

            def new2
            @participant= Participant.new
            end

            def create
            @participant = Participant.create(participant_params)
            @participant.save
            if @participant.save
            flash[:success] = "Successfully Registered!"        

            #email notifes admin of new registration
            NotifyMailer.notify_email(@participant).deliver_later

            redirect_to '/signup'
            end
            end

            def edit
            end

            def update
            end

            def show
            end

            def index
            end

            private
            def participant_params
            params.require(:participant).permit(:first_name, :last_name, :gender, :email, :birthdate, :phone, :street_name, :city, :state, :zip, :nationality, :religion, :need_ride, 
            :has_spouse, :spouse_name, :english_level, :expectations, :length_of_stay, :exact_length, :volunteer_id, :matched, :returned_home, :participant_id, :participant_id_id)

            end


            end

这是服务器错误：

    NoMethodError (undefined method `nationality' for #<Participant:0x000000000d039410>
                            Did you mean?  Rational):

                            app/controllers/participants_controller.rb:11:in `create'
                            Rendering C:/Ruby24-x64/lib/ruby/gems/2.4.0/gems/actionpack-5.0.7.1/lib/action_dispatch/middleware/templates/rescues/diagnostics.html.erb within rescues/layout
                            Rendering C:/Ruby24-x64/lib/ruby/gems/2.4.0/gems/actionpack-5.0.7.1/lib/action_dispatch/middleware/templates/rescues/_source.html.erb
                            Rendered C:/Ruby24-x64/lib/ruby/gems/2.4.0/gems/actionpack-5.0.7.1/lib/action_dispatch/middleware/templates/rescues/_source.html.erb (3.9ms)
                            Rendering C:/Ruby24-x64/lib/ruby/gems/2.4.0/gems/actionpack-5.0.7.1/lib/action_dispatch/middleware/templates/rescues/_trace.html.erb
                            Rendered C:/Ruby24-x64/lib/ruby/gems/2.4.0/gems/actionpack-5.0.7.1/lib/action_dispatch/middleware/templates/rescues/_trace.html.erb (1.0ms)
                            Rendering C:/Ruby24-x64/lib/ruby/gems/2.4.0/gems/actionpack-5.0.7.1/lib/action_dispatch/middleware/templates/rescues/_request_and_response.html.erb
                            Rendered C:/Ruby24-x64/lib/ruby/gems/2.4.0/gems/actionpack-5.0.7.1/lib/action_dispatch/middleware/templates/rescues/_request_and_response.html.erb (1.0ms)
                            Rendered C:/Ruby24-x64/lib/ruby/gems/2.4.0/gems/actionpack-5.0.7.1/lib/action_dispatch/middleware/templates/rescues/diagnostics.html.erb within rescues/layout (790.6ms)

看看是否有人可以帮助澄清我的错误。

谢谢！

Answer 1

有几件事可能会有所帮助

如何定义has_one关系:

跟随 rails guide，因为参与者 has_one student_detail，那么 student_detail table 必须有字段 participant_id，也 volunteer_detail 必须有字段 participant_id

您可以将 participant.rb（模型）设置为接受 student_detail 或 volunteer_detail 的嵌套属性（因为您说过为那些 table 提供一种形式）
```
class Participant < ActiveRecord::Base
  has_one :student_detail, :dependent => :destroy
  accepts_nested_attributes_for :student_detail,   :allow_destroy => :true
  # that allow_destroy is depend with your software design
  has_one :volunteer_detail, :dependent => :destroy
  accepts_nested_attributes_for :volunteer_detail,   :allow_destroy => :true
end
```

如何为其他 table 设置 participant_params：

这里是为接受嵌套属性定义参与者参数的代码示例：

def participant_params
  params.require(:participant).permit(
    :first_name, :other_participant_field_name, 
    student_detail_attributes: [:participant_id, :other_student_field_name],
    volunteer_detail_attributes: [:participant_id, :other_volunteer_field_name])
  end
end

如果你想要学生记录的内容也用于 volunteer_detail 你可以在你的控制器中做（创建方法），我的提示尝试 refactor/redesign 最小化数据在你的系统中重复（学生和志愿者）

def create
  @participant = Participant.create(participant_params)
  @volunteer_detail = @participant.student_detail
  # this will pass all the content of student detail to volunteer detail
  if @participant.save
    flash[:success] = "Successfully Registered!"        
  end
end

要了解更多关于接受嵌套属性我建议你学习railcast 196虽然它看起来很老但是你可以学习这个概念

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