为什么我收到错误 "undefined method `id' for nil:NilClass"，即使 Rails 中有一个 ID？

Question

您好，我正在执行 Rails 邮件操作。

routes.rb:

  resources :textbook_giveaways do
    member do
      get 'contact', to: 'textbook_giveaways#new_contact', as: 'new_contact'
      post 'contact', to: 'textbook_giveaways#send_contact', as: 'send_contact'
    end
  end

new_contact_html.erb:

<div class="container">
<div class="row">
  <h2>ID is: <%= @textbook_giveaway.id %></h2>
  <form role="form" action="" method="post" >
    <!--<div class="col-sm-6">-->
    <!-- <div class="col-sm-offset-4 col-sm-4 col-sm-offset-4"> -->
    <div class="col-sm-offset-4 col-sm-4 col-sm-offset-4">
      <div class="form-group">
        <!--<label for="InputMessage">Message</label>-->
        <div class="input-group">
            <%= form_tag send_contact_textbook_giveaway_path(@texbook_giveaway.id) do %>

                <label><h4>I would like to buy <strong><%=@texbook_giveaway.title%></strong></h4></label>

这一行 <h2>ID is: <%= @textbook_giveaway.id %></h2> 工作正常。它显示了身份证号码。

但是 <%= form_tag send_contact_textbook_giveaway_path(@texbook_giveaway.id) do %> 这给了我错误。

picture 以上是错误图片

当我运行耙路线时，我得到：

new_contact_textbook_giveaway GET    /textbook_giveaways/:id/contact(.:format) textbook_giveaways#new_contact
send_contact_textbook_giveaway POST   /textbook_giveaways/:id/contact(.:format) textbook_giveaways#send_contact
            textbook_giveaways GET    /textbook_giveaways(.:format)             textbook_giveaways#index
                               POST   /textbook_giveaways(.:format)             textbook_giveaways#create
         new_textbook_giveaway GET    /textbook_giveaways/new(.:format)         textbook_giveaways#new
        edit_textbook_giveaway GET    /textbook_giveaways/:id/edit(.:format)    textbook_giveaways#edit
             textbook_giveaway GET    /textbook_giveaways/:id(.:format)         textbook_giveaways#show
                               PATCH  /textbook_giveaways/:id(.:format)         textbook_giveaways#update
                               PUT    /textbook_giveaways/:id(.:format)         textbook_giveaways#update
                               DELETE /textbook_giveaways/:id(.:format)         textbook_giveaways#destroy


  [1]: http://i.stack.imgur.com/MbiUz.png

我的控制器是这样的：

class TextbookGiveawaysController < ApplicationController
  before_action :set_textbook_giveaway, only: [:show, :edit, :update, :destroy, :new_contact, :send_contact]

  # GET /textbook_giveaways
  # GET /textbook_giveaways.json
  def index
    @textbook_giveaways = TextbookGiveaway.all.order(created_at: :desc).paginate(page: params[:page], per_page: 10)
  end

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

  # GET /textbook_giveaways/new
  def new
    @textbook_giveaway = TextbookGiveaway.new
  end

  # GET /textbook_giveaways/1/edit
  def edit
    if not @textbook_giveaway.user_email == current_user.email || current_user.email == "codeinflash@gmail.com"
      redirect_to @textbook_giveaway
    end
  end

  # POST /textbook_giveaways
  # POST /textbook_giveaways.json
  def create
    @textbook_giveaway = TextbookGiveaway.new(textbook_giveaway_params)
    @textbook_giveaway.user_email = current_user.email
    @textbook_giveaway.giveaway = true

    respond_to do |format|
      if @textbook_giveaway.save
        format.html { redirect_to @textbook_giveaway }
        flash[:success] = "Textbook giveaway was successfully created."
      else
        format.html { render :new }
        format.json { render json: @textbook_giveaway.errors, status: :unprocessable_entity }
      end
    end
  end

  # PATCH/PUT /textbook_giveaways/1
  # PATCH/PUT /textbook_giveaways/1.json
  def update
    respond_to do |format|
      if @textbook_giveaway.update(textbook_giveaway_params)
        format.html { redirect_to @textbook_giveaway }
        flash[:success] = 'Textbook giveaway was successfully updated.'
      else
        format.html { render :edit }
        format.json { render json: @textbook_giveaway.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /textbook_giveaways/1
  # DELETE /textbook_giveaways/1.json
  def destroy
    @textbook_giveaway.destroy
    respond_to do |format|
      format.html { redirect_to textbook_giveaways_url }
      format.json { head :no_content }
      flash[:alert] = "Textbook giveaway was successfully destroyed."
    end
  end

  #here for contact
  def new_contact
  end

  def send_contact
    message = params[:message]
    if Contact.send_contact(@textbook_giveaway, current_user, message).deliver
      flash[:success] = "Email sent."
      redirect_to @textbook_giveaway
    else
      flash[:alert] = "There was a problem sending the email."
      render :new_contact
    end
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    def set_textbook_giveaway
      @textbook_giveaway = TextbookGiveaway.friendly.find(params[:id])
    end

    # Never trust parameters from the scary internet, only allow the white list through.
    def textbook_giveaway_params
      params.require(:textbook_giveaway).permit(:title, :subject, :user_email, :description, :giveaway, :slug, :thumbnail)
      #params.fetch(:textbook_giveaway, {})
    end
end

Answer 1

这是您代码中的一个小错字。

这一行是正确的：

<h2>ID is: <%= @textbook_giveaway.id %></h2>

在下面这行中，您拼错了变量名。 @texbook_giveaway 应该是 @textbook_giveaway.

<%= form_tag send_contact_textbook_giveaway_path(@texbook_giveaway.id) do %>

在 Ruby 中调用未分配的实例变量不会引发错误。它只是 returns nil.

为什么我收到错误 "undefined method `id' for nil:NilClass"，即使 Rails 中有一个 ID？

Why am I getting error "undefined method `id' for nil:NilClass" even though there's a id in Rails?

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