頁面中的NoMethodError＃create

Question

嗨，大家好我是Ruby on Rails的新手，當我嘗試添加新頁面時出現錯誤。當我點擊創建這是什麼出現

當你沒有想到它時，你有一個零對象！您可能需要 Array的實例。而評估 nil.collect

class PagesController < ApplicationController 

    layout 'admin'#apply the admin.html layout 

    before_filter :confirm_logged_in #confirms if the user is logged in before entering the page 
    before_filter :find_subject 

    def index 
     list 
     render('list')#runs pages/list.html 
    end 

    def list 
    @pages = Page.where(:subject_id => @subject.id)#for the list view it finds the products sorted,all of them 
    end 

    def show 
    @page = Page.find(params[:id])#it finds the information of the product by its id and shows it in the show.html 
    end 

    def new 
    @page = Page.new(:subject_id => @subject.id)#it creates a new page(product) in the corresponding subject(category) 
    @page_count = @subject.pages.size + 1 #the quantity of total (pages)products all of them 
    @subjects = Subject.order('position ASC')# shows the subjects ordered ascending 
     end 

     def create 
     #new_position = params[:page].delete(:position) 

     @page = Page.new(params[:page]) #instantiate a new object using form parameters 
     puts "Im here" 
     if @page.save# save the object 
     #@page.move_to_position(new_position) 

     flash[:notice] = "Product created." 
     redirect_to(:action => 'list', :subject_id => @page.subject_id)# if save succeeds, redirect to the list action 
    else  
     @page_count = @subject.pages.size + 1 # products quantity is updated 
     @subjects = Subject.order('position ASC') 
     render('new') # if save fails, redisplay the form so user can fix problems 
    end 
    end 

    def edit 
    @page = Page.find(params[:id])# it find the page to be edited by its id 
    @page_count = @subject.pages.size 
    @subjects = Subject.order('position ASC') 
    end 

    def update 
    new_position = params[:page].delete(:position) 

    @page = Page.find(params[:id])# find object using parameters 

    if @page.update_attributes(params[:page])# update the object 
     @page.move_to_position(new_position) 

     flash[:notice] = "Page updated." 
     redirect_to(:action => 'show', :id => @page.id, :subject_id => @page.subject_id)# if update succeeds, redirect to the list action 
    else 

     @page_count = @subject.pages.size 
     @subjects = Subject.order('position ASC') 
     render('edit')# if save fails, redisplay the form so user can fix problems 
    end 
    end 

    def delete 
    @page = Page.find(params[:id])#it finds the page by the id to be deleted 
    end 

    def destroy 
    page = Page.find(params[:id])#it finds the page by the id to be destroyed 
    page.move_to_position(nil) 
    page.destroy 
    flash[:notice] = "Product destroyed." 
    redirect_to(:action => 'list', :subject_id => @subject.id)# redirect the user to the pages/list.html according to the corresponding subject(category) 
    end 

    private 
    def find_subject 
    if params[:subject_id] 
     @subject = Subject.find_by_id(params[:subject_id]) 
    end 
    end 


end 

我可以在任何沒有問題添加主題和我可以毫不問題，問題是網頁添加管理員用戶發生錯誤。

class SubjectsController < ApplicationController 

    layout 'admin'#apply the admin.html layout 

    before_filter :confirm_logged_in #confirms if the user is logged in before entering the page 

    def index 
    list 
    render('list')#runs subjects/list.html all list.html are different 
    end 

    def list 
    @subjects = Subject.order("subjects.position ASC")#for the list view it finds the categories sorted,all of them 
    end 

    def show 
    @subject = Subject.find(params[:id]) 
    end 

    def new 
    @subject = Subject.new # creates a new subject(category) 
    @subject_count = Subject.count + 1 
    end 

    def create 
    new_position = params[:subject].delete(:position) 

    @subject = Subject.new(params[:subject]) # instantiate a new object using form parameters 

    if @subject.save #save the object 

     @subject.move_to_position(new_position) 

     flash[:notice] = "Category created." 
     redirect_to(:action => 'list')# if save succeeds, redirect to list.html 
    else 

     @subject_count = Subject.count + 1 
     render('new')#If save fails, redisplay the form so user can fix problems 
    end 
    end 


    def edit 
    @subject = Subject.find(params[:id])# it finds the subject to be edited 
    @subject_count = Subject.count 
    end 

    def update 
    new_position = params[:subject].delete(:position)#if updated it delete the current position 

    @subject = Subject.find(params[:id])# find object using form parameters 

    if @subject.update_attributes(params[:subject])#update the object(subject) 
     @subject.move_to_position(new_position)#new position assigned 

     flash[:notice] = "Subject updated." 
     redirect_to(:action => 'show', :id => @subject.id)# if update succeeds, redirect to the list action 
    else 

     @subject_count = Subject.count 
     render('edit')# if save fails, redisplay the form so user can fix problems 
    end 
    end 

    def delete 
    @subject = Subject.find(params[:id])#it finds thesubjectby the id to be deleted 
    end 

    def destroy 
    subject = Subject.find(params[:id])#it finds the Subject(category)by the id to be destroyed 
    subject.move_to_position(nil) 
    subject.destroy 
    flash[:notice] = "Subject destroyed." 
    redirect_to(:action => 'list')# redirected to the list.html 
    end 

end 

這是假定誤差根據所述框架 提取的源被happenign的_form.html.erb（圍繞線＃6）：

3: <table summary="Products form fields"> 
4: <tr> 
5:  <th><%= f.label(:subject_id, "Category") %></th> 
6: <td><%= f.select(:subject_id, @subjects.collect {|s| [s.name, s.id]}) %></td> </tr> 

<%= error_messages_for(@pages) %> 

<table summary="Products form fields"> 
    <tr> 
    <th><%= f.label(:subject_id, "Category") %></th> 
    <td><%= f.select(:subject_id, @subjects.collect {|s| [s.name, s.id]}) %></td> </tr> 
    <tr> 
    <th><%= f.label(:product_name) %></th> 
    <td><%= f.text_field(:product_name) %></td> 
    </tr> 
    <tr> 
    <th><%= f.label(:description) %></th> 
    <td><%= f.text_area(:description) %></td> 
    </tr> 
    <tr> 
    <th><%= f.label(:min_description) %></th> 
    <td><%= f.text_area(:min_description) %></td> 
    </tr> 
    <tr> 
    <th><%= f.label(:brand) %></th> 
    <td><%= f.text_field(:brand) %></td> 
    <tr> 
    <th><%= f.label(:quantity) %></th> 
    <td><%= f.text_field(:quantity) %></td> 
    </tr> 
    <tr> 
    <th><%= f.label(:price) %></th> 
    <td><%= f.text_field(:price) %></td> 
    </tr> 
    <tr> 
    <th><%= f.label(:size) %></th> 
    <td><%= f.text_field(:size) %></td> 
    </tr> 
    <tr> 
    <th><%= f.label(:head_size) %></th> 
    <td><%= f.text_field(:head_size) %></td> 
    </tr> 
    <tr> 
    <th><%= f.label(:racquets_weight) %></th> 
    <td><%= f.text_field(:racquets_weight) %></td> 
    </tr> 
    <tr> 
    <th><%= f.label(:category) %></th> 
    <td><%= f.text_field(:category) %></td> 
    </tr> 
    <tr> 
    <th><%= f.label(:image_url) %></th> 
    <td><%= f.text_field(:image_url) %></td> 

    </tr> 
</table> 

框架跟蹤

actionpack（3.0.9）lib/action_view/template.rb：135：send' actionpack (3.0.9) lib/action_view/template.rb:135:in render' activesupport（3.0.9）lib/active_support/notifications.rb：54： instrument' actionpack (3.0.9) lib/action_view/template.rb:127:in 渲染 'ActionPack的（3.0.9）LIB/ACTION_VIEW /渲染/ partials.rb：333：在 render_partial' actionpack (3.0.9) lib/action_view/render/partials.rb:262:in渲染' 的ActiveSupport （3.0.9）LIB/active_support/notifications.rb：52：在instrument' activesupport (3.0.9) lib/active_support/notifications/instrumenter.rb:21:in儀器」 的ActiveSupport （3.0.9）lib/active_support/notifications.rb：52：in instrument' actionpack (3.0.9) lib/action_view/render/partials.rb:260:in render'actionpack（3.0.9） lib/action_view/render/partials.rb：378：in _render_partial' actionpack (3.0.9) lib/action_view/render/rendering.rb:22:in render'actionpack （3.0.9） lib/action_view/helpers/capture_helper.rb：40：在capture' actionpack (3.0.9) lib/action_view/helpers/form_helper.rb:545:in fields_for' actionpack（3.0.9）lib/action_view/40：在capture' actionpack (3.0.9) lib/action_view/helpers/capture_helper.rb:172:in with_output_buffer'actionpack（3.0.9） lib/action_view/helpers/capture_helper.rb：幫手/ form_helper.rb：320：在0123中（3.0.9）lib/action_view/template.rb：127： render' actionpack (3.0.9) lib/action_view/render/rendering.rb:59:in _render_template'activesupport（3.0.9）lib/action_view/template.rb：135：render' activesupport (3.0.9) lib/active_support/notifications.rb:54:in ） lib/active_support/notifications.rb：52：in instrument' activesupport (3.0.9) lib/active_support/notifications/instrumenter.rb:21:in instrument'activesupport（3.0.9） lib/active_support/notifications.rb：52：in instrument' actionpack (3.0.9) lib/action_view/render/rendering.rb:56:in _render_template' actionpack（3.0.9）lib/action_view/render/render.rb：26：render' actionpack (3.0.9) lib/abstract_controller/rendering.rb:115:in _render_template'actionpack（3.0.9） lib/abstract_controller/rendering.rb：109：render_to_body' actionpack (3.0.9) lib/action_controller/metal/renderers.rb:47:in render_to_body'actionpack（3.0.9） lib/action_controller/metal/compatibility.rb：55：在render_to_body' actionpack (3.0.9) lib/abstract_controller/rendering.rb:102:in render_to_strin g'actionpack（3.0.9） lib/abstract_controller/rendering.rb：93：in render' actionpack (3.0.9) lib/action_controller/metal/rendering.rb:17:in render'actionpack （3.0.9）lib/action_controller/metal/instrumentation.rb：40：in render' activesupport (3.0.9) lib/active_support/core_ext/benchmark.rb:5:in ms'c：/ RailsInstaller /Ruby1.8.7/lib/ruby/1.8/benchmark.rb:308:in realtime' activesupport (3.0.9) lib/active_support/core_ext/benchmark.rb:5:in ms'actionpack（3.0.9） lib/action_controller/metal/instrumentation.rb：40：in render' actionpack (3.0.9) lib/action_controller/metal/instrumentation.rb:78:in cleanup_view_runtime'activerecord（3.0.9 ） LIB/active_record/railties/controller_runtime.rb：15：在 cleanup_view_runtime' actionpack (3.0.9) lib/action_controller/metal/instrumentation.rb:39:in渲染 ' ActionPack的（3.0.9）LIB/action_controller /金屬/ implicit_render.rb：4： send_action' actionpack (3.0.9) lib/action_controller/metal/implicit_render.rb:4:in send_action' ActionPack的（3.0。9）LIB/abstract_controller/base.rb：150：在 process_action' actionpack (3.0.9) lib/action_controller/metal/rendering.rb:11:in process_action」 ActionPack的（3.0.9）LIB/abstract_controller/callbacks.rb：18：在 process_action' activesupport (3.0.9) lib/active_support/callbacks.rb:446:in 運行 _367793087__process_action_ _callbacks'的ActiveSupport （3.0 .9）lib/active_support/callbacks.rb：410：send' activesupport (3.0.9) lib/active_support/callbacks.rb:410:in _run_process_action_callbacks'activesupport（3.0.9） lib/active_support/callbacks.rb：94：in send' activesupport (3.0.9) lib/active_support/callbacks.rb:94:in run_callbacks'actionpack （3.0.9）lib/abstract_controller/callbacks .rb：17：process_action' actionpack (3.0.9) lib/action_controller/metal/instrumentation.rb:30:in process_action' activesupport（3.0.9）lib/active_support/notifications.rb：52：in instrument' activesupport (3.0.9) lib/active_support/notifications/instrumenter.rb:21:in儀器 ' 的ActiveSupport（3.0.9）LIB/active_support/notifications.rb：52：在 instrument' actionpack (3.0.9) lib/action_controller/metal/instrumentation.rb:29:in process_action' ActionPack的（3.0.9）LIB/action_controller /金屬/ rescue.rb：17：在 process_action' actionpack (3.0.9) lib/abstract_controller/base.rb:119:in過程ActionPack的（3.0.9） lib/abstract_controller/rendering.rb：41：in process' actionpack (3.0.9) lib/action_controller/metal.rb:138:in dispatch'actionpack （3.0.9）lib/action_controller/metal/rack_delegation.rb：14：in dispatch' actionpack (3.0.9) lib/action_controller/metal.rb:178:in action'actionpack（3.0.9） lib/action_dispatch/routing/route_set.rb：62：call' actionpack (3.0.9) lib/action_dispatch/routing/route_set.rb:62:in dispatch' actionpack（3.0.9）lib/action_dispatch/routing/route_set.rb：27：in call' rack-mount (0.6.14) lib/rack/mount/route_set.rb:148:in call' 機架安裝（0.6.14）lib/rack/mount/code_generation.rb：93：在 recognize' rack-mount (0.6.14) lib/rack/mount/code_generation.rb:75:in optimized_each'機架安裝 （0.6.14）lib/rack/mount/code_generation.rb：92：在recognize' rack-mount (0.6.14) lib/rack/mount/route_set.rb:139:in調用' ActionPack的（3.0.9）LIB/action_dispatch /路由/ route_set.rb：493：在 call' actionpack (3.0.9) lib/action_dispatch/middleware/best_standards_support.rb:17:in呼叫' ActionPack的（3.0.9）LIB/action_dispatch /中間件/ head.rb：14：call' rack (1.2.8) lib/rack/methodoverride.rb:24:in呼叫」 ActionPack的 （3.0.9）lib/action_dispatch/middleware/params_parser.rb：21：在call' actionpack (3.0.9) lib/action_dispatch/middleware/flash.rb:182:in 調用'actionpack（3.0.9） lib/action_dispatch/middleware/session/abstract_store.rb：149：在call' actionpack (3.0.9) lib/action_dispatch/middleware/cookies.rb:302:in 調用'activerecord（3.0。 9）lib/active_record/query_cache.rb：32：在 call' activerecord (3.0.9) 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tap'railties（3.0.9）lib/rails/commands.rb：27 script /軌道：6：在 `要求'腳本/導軌：6

任何形式的幫助讚賞。

Answer 1

確保你總是仔細閱讀錯誤，他們是理解錯誤的關鍵。在這裏你的錯誤說：

你有沒有對象，當你沒有想到它！您可能預期了Array的一個實例。評估nil收集時發生錯誤

這告訴我們在你的代碼的某個地方，你在一個零對象上調用collect。由於您沒有明確地在任何地方撥打nil.collect，因此假設您可能呼叫@some_instance_variable_that_is_not_set.collect是安全的。從那裏你應該看看它正在抱怨的行號（在本例中是第6行），並找到你要調用collect的變量，那可能是零。在這裏，你會發現@subjects.collect這是可能的罪魁禍首。將puts @subjects添加到您的控制器並檢查日誌以查看輸出結果。如果它爲零，則不會在控制器的create方法中設置該值。

這是您在瀏覽錯誤消息時應始終採用的方法。