ruby-on-rails - 错误 : undefined method `each' for nil:NilClass

Question

我收到此错误:undefined method `each' for nil:NilClass 尝试呈现 choose_album_to_add.html.erb 时:

<table class="table_">
  <thead>
    <tr>
      <th>Album</th>
    </tr>
  </thead>

  <tbody>
    <% @albums.each do |album| %>
      <tr>
        <td><%= album.name %></td>
      </tr>
    <% end %>
  </tbody>
</table>

<br>

我的users_controller.rb

def choose_album_to_add
       @albums = Album.all
end

有什么问题吗？编辑

根据要求，我确定我的 View 文件 choose_album_to_add.html.erb 位于/app/views/users 中。我有这样一条路线:

将“/addAlbum/:id”匹配到:“users#choose_album_to_add”，通过:“get”

当然，我在浏览器上输入/addAlbum/45，它会正确路由。 View 也肯定会加载，但问题是我在 Controller 上声明的实例变量无法在我的 View 上访问。 =[

我已经构建了四个资源，它们按照声明实例变量并在 View 中使用 then 的约定工作得很好。我知道有其他方法(比如路过本地人)，但我想以这种方式完成这项工作。

尝试访问时来自控制台的日志

Started GET "/addAlbum/50" for 127.0.0.1 at 2014-03-24 09:56:13 -0400
Processing by UsersController#choose_album_to_add as HTML
  Parameters: {"id"=>"50"}
  Rendered users/choose_album_to_add.html.erb within layouts/application (1.0ms)
Completed 500 Internal Server Error in 3ms

ActionView::Template::Error (undefined method `each' for nil:NilClass):
    14:   </thead>
    15: 
    16:   <tbody>
    17:     <% @albums.each do |album| %>
    18:       <tr>
    19:         <td><%= album.name %></td>
    20:         <td><%= album.created_on %></td>
  app/views/users/choose_album_to_add.html.erb:17:in `_app_views_users_choose_album_to_add_html_erb___3017203676622264637_69974786999340'

当我在控制台上运行 Album.all 时，我得到:

SELECT "albums".* FROM "albums"
 => #<ActiveRecord::Relation [#<Album id: 1, name: "Album1", created_on: "2014-03-17 23:33:00", finishes_on: "2014-03-24 13:16:00", created_at: "2014-03-17 23:33:14", updated_at: "2014-03-24 13:16:32">, #<Album id: 2, name: "Album2", created_on: "2014-03-17 23:33:00", finishes_on: "2014-03-24 13:16:00", created_at: "2014-03-17 23:33:28", updated_at: "2014-03-24 13:16:42">]> 

这是我通过脚手架生成的 Rest 方法插入的两个元组。

users_controller.rb

class UsersController < ApplicationController
  before_action :set_user, only: [:show, :edit, :update, :destroy]

  # GET /users
  # GET /users.json
  def index
    @users = User.all
  end

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

  # GET /users/new
  def new
    @user = User.new
  end

  # GET /users/1/edit
  def edit
  end

  # POST /users
  # POST /users.json
  def create
    @user = User.new(user_params)
    @user.photographer_id = session[:current_photographer_id]

    respond_to do |format|
      if @user.save
        format.html { redirect_to @user, notice: 'Novo usuário cadastrado com sucesso. Um email foi encaminhado a ele contendo as informações de acesso.' }
        format.json { render action: 'show', status: :created, location: @user }
      else
        format.html { render action: 'new' }
        format.json { render json: @user.errors, status: :unprocessable_entity }
      end
    end
  end

  # PATCH/PUT /users/1
  # PATCH/PUT /users/1.json
  def update
    respond_to do |format|
      if @user.update(user_params)
        format.html { redirect_to @user, notice: 'Dados atualizados com sucesso' }
        format.json { head :no_content }
      else
        format.html { render action: 'edit' }
        format.json { render json: @user.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /users/1
  # DELETE /users/1.json
  def destroy
    @user.destroy
    respond_to do |format|
      format.html { redirect_to users_url }
      format.json { head :no_content }
    end
  end

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

    # Never trust parameters from the scary internet, only allow the white list through.
    def user_params
      params.require(:user).permit(:name, :email, :password, :endereco, :telefone, :cpf)
    end

    def choose_album_to_add
       @albums = Album.all
    end

  end
end

还有约会吗？谢谢

Answer 1

您的方法 def choose_album_to_add 是私有(private)的 - 将定义移至 private 语句之上。

因为 choose_album_to_add 是一个 Action ，所以必须是 View 使用的公共(public)方法。我认为您已经证明当您尝试设置 @albums = 1 时没有调用该方法并且它没有任何区别。