返回 nil:NilClass 的未定义方法“每个”？

Question

这是我在视图中的代码：show.html.erb

<ul>
<% @bullets.each do |r| %>
    <li><%= r.content %></li>
<% end %>
</ul>

这是我在控制器中的代码：users_controller.rb

if cookies[:bullets].nil?
  @bullets = Bullet.all.shuffle.first(4)
  cookies[:bullets] = @bullets.collect(&:id)
else
 @bullets = []
 cookies[:bullets].each do |id|
   @bullets << Bullet.find(id)
 end
end

这将为 nil:NilClass 返回未定义的方法 'each'

<% @bullets.each do |r| %>

我想知道它为什么这样做，以及如何修复它以从名为“bullets”的数据库 (sqlite3) 表中发布四个随机固定的项目符号内容（列是内容）。

编辑：这是整个控制器：

class StudentsController < ApplicationController
    #GET /
    def index
      @students = Student.all 

      respond_to do |format|
        format.html # index.html.erb
        format.json { render json: @students }
        end  
    end 

    #GET /new
    def new 
      @student = Student.new
    end 

    #POST
    def create
      @student = Student.new(params[:student])
          if @student.save
        render :file => 'app/views/success'
      else 
        render :file => 'app/views/students/fail'
      end  
        end

    #GET /students/{:id}
    def show 
       @student = Student.find_by_url(params[:id])

           respond_to do |format|
         format.html # show.html.erb
         format.json { render json: @student } 
           end  
    end

    #BULLETS Randomizing /students/new.html.erb
    if cookies[:bullets].nil?
      @bullets = Bullet.all.shuffle.first(4)
      cookies[:bullets] = @bullets.collect(&:id)
    else
     @bullets = []
     cookies[:bullets].each do |id|
       @bullets << Bullet.find(id)
     end
    end

    #GET /students/1/edit
    def edit 
        @student = Student.find_by_url(params[:id])
    end 

    def update
      @student = Student.find_by_url(params[:id])
      respond_to do |format|
        if @student.update_attributes(params[:student])
          format.html { redirect_to @student, notice: 'Student was successfully updated.'}  
        else 
          format.html { render action: "edit" } 
          format.json { render json: @student.errors, status: :unprocessable_entity } 
        end 
        end 
    end 

    #DELETE
    def destroy 
    @student = Student.find_by_url(params[:id])
    @student.destroy

        respond_to do |format|
         format.html { redirect_to students_url }
         format.json { head :no_content }
        end
    end
end 

编辑#2：像这样？

#GET /students/{:id}
    def show 
       @student = Student.find_by_url(params[:id])

        #BULLETS Randomizing /students/show.html.erb
    if cookies[:bullets].nil?
      @bullets = Bullet.all.shuffle.first(4)
      cookies[:bullets] = @bullets.collect(&:id)
    else
     @bullets = []
     cookies[:bullets].each do |id|
       @bullets << Bullet.find(id)
     end
    end

           respond_to do |format|
         format.html # show.html.erb
         format.json { render json: @student } 
           end  
    end

Answer 1

看起来应该是：

#GET /students/{:id}
def show 

   @student = Student.find_by_url(params[:id])

   #BULLETS Randomizing /students/new.html.erb
   if cookies[:bullets].nil?
     @bullets = Bullet.all.shuffle.first(4)
     cookies[:bullets] = @bullets.collect(&:id)
   else
     # simpler to use an 'in list' for only 4 id's
     Bullet.where("id in (?)", cookies[:bullets])
   end

   respond_to do |format|
     format.html # show.html.erb
     format.json { render json: @student } 
   end  
end

请注意，我将您在 cookies 数组上的循环转换为带有“in list”的单个语句——这应该会简化为查找生成的 sql。

虽然，这段代码应该被推入模型是有争议的：

class Bullet < ActiveRecord::Base

  NUM_USER_BULLETS = 4
  # fetch a random set of 
  def self.user_bullets
    Bullet.all.shuffle.first(NUM_USER_BULLETS)
  end
end

或类似的东西。那么你的控制器就更简单了：

#GET /students/{:id}
def show 

   @student = Student.find_by_url(params[:id])

   #BULLETS Randomizing /students/new.html.erb
   if cookies[:bullets].nil?
     @bullets = Bullet.user_bullets
     cookies[:bullets] = @bullets.collect(&:id)
   else
     # simpler to use an 'in list' for only 4 id's
     Bullet.where("id in (?)", cookies[:bullets])
   end

   respond_to do |format|
     format.html # show.html.erb
     format.json { render json: @student } 
   end  
end

将代码迁移到您的模型中后，您的控制器就更简单了。

Answer 2

class StudentsController < ApplicationController
   before_filter :get_bullets, :only => [:show]


  def show

  end

  ... 


  protected

  def get_bullets
  #BULLETS Randomizing /students/new.html.erb
    if cookies[:bullets].nil?
      @bullets = Bullet.all.shuffle.first(4)
      cookies[:bullets] = @bullets.collect(&:id)
    else
     @bullets = []
     cookies[:bullets].each do |id|
       @bullets << Bullet.find(id)
     end
    end

  end



end

Answer 3

我建议将您的“随机项目符号”代码重构为 before_filter 以用于 show 操作并在数据库中执行随机化，这将比加载整个表并在 Ruby 中执行随机化更快：

class UsersController < ApplicationController
  before_filter :assign_bullets, :only => :show

  # ...

private

  def assign_bullets
    if cookies[:bullets]
      @bullets = cookies[:bullets].map { |id| Bullet.find(id) }
    else
      @bullets = Bullet.order('RANDOM()').limit(4)
      cookies[:bullets] = @bullets.map(&:id)
    end
  end
end