Rails：在创建后关联一个对象

Question

我正在尝试创建一个会显示分步说明的网站。用户将查看问题并选择答案。答案视图如下所示：

<p id="notice"><%= notice %></p> 

<p> 
    <strong>Post:</strong> 
    <%= @question.post %> 
</p> 

<%= link_to 'Answer', new_step_path(:question_id=>@question.id) %> | 
<%= link_to 'Edit', edit_question_path(@question) %> | 
<%= link_to 'Back', questions_path %> 

当用户选择“答案”时，我重定向到步骤＃new，它呈现了步骤表单。

<%= form_for(@step) do |f| %> 
    <% if @step.errors.any? %> 
    <div id="error_explanation"> 
     <h2><%= pluralize(@step.errors.count, "error") %> prohibited this step from being saved:</h2> 

     <ul> 
     <% @step.errors.full_messages.each do |msg| %> 
     <li><%= msg %></li> 
     <% end %> 
     </ul> 
    </div> 
    <% end %> 

    <div class="actions"> 
    <%= @question.id %> 
    <%= f.hidden_field :question_id, :value => @question.id %> 
    </div> 

    <div class="field"> 
    <%= f.label :post %><br> 
    <%= f.text_field :post %> 
    </div> 
    <div class="actions"> 
    <%= f.submit %> 
    </div> 
<% end %> 

我通过在URL，然后进入一个隐藏字段的相关问题。

鉴于步骤has_many：questions，：through =>：instruction，在步骤控制器创建Step之后，如何将隐藏的字段值插入到Instructions模型中？

class StepsController < ApplicationController 
    before_action :set_step, only: [:show, :edit, :update, :destroy] 

    # GET /steps 
    # GET /steps.json 
    def index 
    @steps = Step.all 
    end 

    # GET /steps/1 
    # GET /steps/1.json 
    def show 
    end 

    # GET /steps/new 
    def new 
    @step = Step.new 
    @question = Question.find(params[:question_id]) 
    end 

    # GET /steps/1/edit 
    def edit 
    end 

    # POST /steps 
    # POST /steps.json 
    def create 
    @step = Step.new(step_params) 

    respond_to do |format| 
     if @step.save 
     @instruction = Instruction.create(:question_id=>@question, :step_id=>@step, :order=>1) 

     format.html { redirect_to @step, notice: 'Step was successfully created.' } 
     format.json { render action: 'show', status: :created, location: @step } 
     else 
     format.html { render action: 'new' } 
     format.json { render json: @step.errors, status: :unprocessable_entity } 
     end 
    end 
    end 

    # PATCH/PUT /steps/1 
    # PATCH/PUT /steps/1.json 
    def update 
    respond_to do |format| 
     if @step.update(step_params) 
     format.html { redirect_to @step, notice: 'Step was successfully updated.' } 
     format.json { head :no_content } 
     else 
     format.html { render action: 'edit' } 
     format.json { render json: @step.errors, status: :unprocessable_entity } 
     end 
    end 
    end 

    # DELETE /steps/1 
    # DELETE /steps/1.json 
    def destroy 
    @step.destroy 
    respond_to do |format| 
     format.html { redirect_to steps_url } 
     format.json { head :no_content } 
    end 
    end 

    private 
    # Use callbacks to share common setup or constraints between actions. 
    def set_step 
     @step = Step.find(params[:id]) 
    end 

    # Never trust parameters from the scary internet, only allow the white list through. 
    def step_params 
     params.require(:step).permit(:post) 
    end 
end 

Answer 1

虽然我问你为模型的关系仍然不清楚这三种模式是如何相互关联的（你只提到：步骤的has_many：问题，：通过=>：指令）。无论如何，我基于我的假设回答你的问题。所以，要小心：
该机型：

class Step < ActiveRecord::Base 
    belongs_to :instruction 
    has_many :questions, 
    through: :instruction 
end 

class Instruction < ActiveRecord::Base 
    has_many :steps 
    has_many :questions 
end 

class Question < ActiveRecord::Base 
    belongs_to :instruction 
end 

，现在你steps_controller.rb：哪里是@question在你的代码实例：
首先？

@instruction = Instruction.create(:question_id=>@question, :step_id=>@step, :order=>1) 

这条线也是但从REST一点上是非常混乱：
一个StepsController＃创建为什么要这么做创建的指令？
如果您无法以其他方式处理它，请将其放入Step模型回调中。你会想它也但从事务点;）
这就是为什么你的行动应该更加类似于：

def create 
    @step = Step.new(step_params) 
    respond_to do |format| 
    if @step.save 
     format.html { redirect_to @step, notice: 'Step was successfully created.' } 
     format.json { render action: 'show', status: :created, location: @step } 
    else 
     format.html { render action: 'new' } 
     format.json { render json: @step.errors, status: :unprocessable_entity } 
    end 
    end 
end 

因此步骤模型：

class Step < ActiveRecord::Base 
    belongs_to :instruction 
    has_many :questions, 
    through: :instruction 
    attr_accessor :question_id 
    before_create :create_related_instruction 

    private 
    def create_related_instruction 
    self.create_instruction question_id: question_id, order: 1 
    end 
end 

我觉得你的想法。