rails 3 undefined 方法 'update_attributes' for nil：nilClass

Question

我是Ruby和rails的新手。我正在做一个更新表单：硬件数据库中的所有者值。在使用自定义视图名称transfer.html.erb时，我的表单代码如下所示。

<%= form_for @hardware, :url => do_transfer_path do |f| %>

这是我在hardwares_ranfers_controller.rb 中的自定义控制器

def transfer
  @hardware = Hardware.find(params[:id])
   if current_user.user_lvl == 0
   @users = User.order(:user_lvl)
   else
   @users = User.where(:refer => current_user.id)
  respond_to do |format|
   format.html # index.html.erb
   format.json { render json: @hardwares }
   end
  end
end

def do_transfer
#    transfer_user = User.where(:id => @hardware.owner).email
#      TransferLog.create([:user_id => current_user.id, :hardware_id => @hardware.id])
  if @hardware.update_attributes(params[:hardware])
    format.html { redirect_to users_url, notice: "Hardware was successfully transfer"}
    format.json { head :no_content }
  else
    format.html { render action: "edit" }
    format.json { render json: @hardware.errors, status: :unprocessable_entity }
  end
end

我得到的错误是HardwareTransfersController#do_transfer中的NoMethodError未定义的方法update_attributes' for nil:NilClass Aplication Traces app/controllers/hardwares_transfers_controller.rb:23:in do_transfer'

参数

{"utf8"=>"✓",
 "_method"=>"put",
 "authenticity_token"=>"vkwKyuS4eviRN1ogrpOcGh1Y5OBNX0wiBzpV8taNkq0=",
 "hardware"=>{"owner"=>"3"},
 "commit"=>"Transfer Hardware"}

我的路线.rb

match "hardwares_transfers/" => "hardwares_transfers#do_transfer" , :as => :do_transfer
get "hardwares_transfers/:id/transfer" => "hardwares_transfers#transfer", :as => :transfer_hardwares

耙路>

       do_transfer        /hardwares_transfers(.:format)              hardwares_transfers#do_transfer
transfer_hardwares GET    /hardwares_transfers/:id/transfer(.:format) hardwares_transfers#transfer
         hardwares GET    /hardwares(.:format)                        hardwares#index
                   POST   /hardwares(.:format)                        hardwares#create
      new_hardware GET    /hardwares/new(.:format)                    hardwares#new
     edit_hardware GET    /hardwares/:id/edit(.:format)               hardwares#edit
          hardware GET    /hardwares/:id(.:format)                    hardwares#show
                   PUT    /hardwares/:id(.:format)                    hardwares#update
                   DELETE /hardwares/:id(.:format)                    hardwares#destroy

Answer 1

您需要

def do_transfer
  @hardware = Hardware.find(params[:id])
  ...
end

我还将借此机会指出，您可能会以更REST的方式构建

Answer 2

查找硬件项：

def do_transfer
  @hardware = Hardware.find(params[:id])
  ...
end

和更改路线。rb:

match "hardwares_transfers/:id" => "hardwares_transfers#do_transfer" , :as => :do_transfer

Answer 3

错误为NoMethodError in HardwaresTransfersController#do_transfer
nil:NilClass的未定义方法update_attributes'。

正如错误所说，Rails试图在nil:NilClass上调用update_attributes，这意味着您的@hardware对象是nil
所以，你应该通过初始化它

@hardware = Hardware.find(params[:id])

你应该经常观察错误，并思考为什么会出现这种错误，这将帮助你更好地学习。