NoMethodError Rails 3.2

Question

我一直在搜索遍地，無法找到任何地方的答案。

我正在參加RoR課程的udemy課程介紹，我已經能夠解決我在課程的前80％所遇到的所有問題，但現在我在路障中，可以找不到這個。我們正在構建一個類似Etsy的應用程序，而且我正需要限制用戶編輯/刪除不屬於他們的列表。

我on Rails的Ruby的運行3.2.21 1.9.3

我嘗試以下，用於將檢查用戶過濾器的指令，但是當我檢查回本地主機上，我收到此錯誤：

NoMethodError in ListingsController#edit

undefined method `user' for nil:NilClass

app/controllers/listings_controller.rb:98:in `check_user'

Parameters: {"id"=>"8"}

我的代碼教練的代碼完全匹配，但我認爲這是錯誤，因爲我使用Rails 3，和他用4

這裏是我的listings_controller.rb

class ListingsController < ApplicationController 
    # GET /listings 
    # GET /listings.json 
    before_filter :authenticate_user!, only: [:new, :create, :edit, :update, :destroy] 
    before_filter :check_user, only: [:edit, :update, :destroy] 

    def index 
    @listings = Listing.all 

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

    # GET /listings/1 
    # GET /listings/1.json 
    def show 
    @listing = Listing.find(params[:id]) 

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

    # GET /listings/new 
    # GET /listings/new.json 
    def new 
    @listing = Listing.new 

    respond_to do |format| 
     format.html # new.html.erb 
     format.json { render json: @listing } 
    end 
    end 

    # GET /listings/1/edit 
    def edit 
    @listing = Listing.find(params[:id]) 
    end 

    # POST /listings 
    # POST /listings.json 
    def create 
    @listing = Listing.new(params[:listing]) 
    @listing.user_id = current_user.id 

    respond_to do |format| 
     if @listing.save 
     format.html { redirect_to @listing, notice: 'Listing was successfully created.' } 
     format.json { render json: @listing, status: :created, location: @listing } 
     else 
     format.html { render action: "new" } 
     format.json { render json: @listing.errors, status: :unprocessable_entity } 
     end 
    end 
    end 

    # PUT /listings/1 
    # PUT /listings/1.json 
    def update 
    @listing = Listing.find(params[:id]) 

    respond_to do |format| 
     if @listing.update_attributes(params[:listing]) 
     format.html { redirect_to @listing, notice: 'Listing was successfully updated.' } 
     format.json { head :no_content } 
     else 
     format.html { render action: "edit" } 
     format.json { render json: @listing.errors, status: :unprocessable_entity } 
     end 
    end 
    end 

    # DELETE /listings/1 
    # DELETE /listings/1.json 
    def destroy 
    @listing = Listing.find(params[:id]) 
    @listing.destroy 

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

    private 
    def set_listing 
    @listing = Listing.find(params[:id]) 
    end 

    def listing_params 
    params.require(:listing).permit(:name, :description, :price, :image) 
    end 

    def check_user 
    if current_user != @listing.user 
     redirect_to root_url, alert: "Sorry, this listing belongs to someone else." 
    end 
    end 

end 

，我們不得不添加該代碼，這是第二次的before_filter和DEF check_user

如果需要任何其他信息，以幫助回答這個問題，請讓我知道。

Answer 1

這不是Rails 3 vs 4問題，你的代碼永遠不會調用set_listing，所以@listing永遠不會被設置。你或許應該有一個：

before_filter :set_listing, only: [:show, :edit, :update, :destroy] 

在你的文件的頂部，前before_filter :check_user, ...