ruby-on-rails - 为什么这些删除操作不起作用？未定义方法 `destroy' 为 nil :NilClass Rails

Question

我正在尝试删除 Rails 中的一个对象，它是作业类的子对象。

%tbody
        -if @job.job_delivery_costs.any?
          -@job.job_delivery_costs.each do |delivery_cost|
            %tr
              %td
                =delivery_cost.timing
              %td
                =delivery_cost.quantity
              %td
                =delivery_cost.cost_per_unit
              %td
                =delivery_cost.quantity * delivery_cost.cost_per_unit
              %td
                =link_to 'Delete', admin_job_job_delivery_cost_path(@job, delivery_cost), method: :delete, class: "btn btn-xs btn-danger"

路线.rb

resources :jobs do
      member do
      resources :job_delivery_costs
      resources :extra_costs, only: [:create, :destroy]

Controller

before_action :get_job

def destroy
    if @job && get_job_delivery_cost
      @get_job_delivery_cost.destroy
      flash[:success] = "Job delivery cost removed"
    else
      flash[:error] = "Couldn't find the record"
    end
    redirect_to admin_job_job_products_path(@job)
  end

  private

    def get_job
        @job = Job.find_by(id: params[:job_id])
    end

    def job_delivery_cost_params
      params.require(:job_delivery_cost).permit!
    end

    def get_job_delivery_cost
        @job_delivery_cost ||= JobDeliveryCost.where(id: params[:id]).first
    end

end


rake routes

rep delivery_cost
                                   job_delivery_costs_new GET    /job_delivery_costs/new(.:format)                                                   job_delivery_costs#new
                                     admin_delivery_costs GET    /admin/delivery_costs(.:format)                                                     admin/delivery_costs#index
                                                          POST   /admin/delivery_costs(.:format)                                                     admin/delivery_costs#create
                                  new_admin_delivery_cost GET    /admin/delivery_costs/new(.:format)                                                 admin/delivery_costs#new
                                 edit_admin_delivery_cost GET    /admin/delivery_costs/:id/edit(.:format)                                            admin/delivery_costs#edit
                                      admin_delivery_cost GET    /admin/delivery_costs/:id(.:format)                                                 admin/delivery_costs#show
                                                          PATCH  /admin/delivery_costs/:id(.:format)                                                 admin/delivery_costs#update
                                                          PUT    /admin/delivery_costs/:id(.:format)                                                 admin/delivery_costs#update
                                                          DELETE /admin/delivery_costs/:id(.:format)                                                 admin/delivery_costs#destroy
                             admin_job_job_delivery_costs GET    /admin/jobs/:job_id/job_delivery_costs(.:format)                                    admin/job_delivery_costs#index
                                                          POST   /admin/jobs/:job_id/job_delivery_costs(.:format)                                    admin/job_delivery_costs#create
                          new_admin_job_job_delivery_cost GET    /admin/jobs/:job_id/job_delivery_costs/new(.:format)                                admin/job_delivery_costs#new
                         edit_admin_job_job_delivery_cost GET    /admin/jobs/:job_id/job_delivery_costs/:id/edit(.:format)                           admin/job_delivery_costs#edit
                              admin_job_job_delivery_cost GET    /admin/jobs/:job_id/job_delivery_costs/:id(.:format)                                admin/job_delivery_costs#show
                                                          PATCH  /admin/jobs/:job_id/job_delivery_costs/:id(.:format)                                admin/job_delivery_costs#update
                                                          PUT    /admin/jobs/:job_id/job_delivery_costs/:id(.:format)                                admin/job_delivery_costs#update
                                                          DELETE /admin/jobs/:job_id/job_delivery_costs/:id(.:format)                                admin/job_delivery_costs#destroy

我肯定在这里传递了正确的参数。如果它要进入销毁条件，它必须找到对象，否则它只会渲染找不到对象。

但是我得到了这个错误

if @job 
      @job_delivery_cost ||= JobDeliveryCost.where(id: params[:id]).first
      @get_job_delivery_cost.destroy
      flash[:success] = "Job delivery cost removed"
    else
      flash[:error] = "Couldn't find the record"
    end
    redirect_to admin_job_job_products_path(@job)

Answer 1

您在错误的对象上调用了 .destroy 方法，改为在 @job_delivery_cost 对象上调用它:

def destroy
  if @job && get_job_delivery_cost
    @job_delivery_cost.destroy
    flash[:success] = "Job delivery cost removed"

---

我可以为您的代码提出一些建议吗？我认为它应该更一致一些，如下所示:

def destroy
  set_job_delivery_cost # will set the variable `@job_delivery_cost`
  if @job.present? && @job_delivery_cost.present?
    @job_delivery_cost.destroy
    flash[:success] = "Job delivery cost removed"
  else
    flash[:error] = "Couldn't find the record"
  end
  redirect_to admin_job_job_products_path(@job)
end

private

def set_job
  @job = Job.find_by(id: params[:job_id])
end

def set_job_delivery_cost
  @job_delivery_cost ||= JobDeliveryCost.find_by(id: params[:id])
end

def job_delivery_cost_params
  params.require(:job_delivery_cost).permit!
end

如您所见，我将方法 get_job 和 get_job_delivery_cost 重命名为 set_job 和 set_job_delivery_cost。该方法本身表示它的执行会引发其变量的声明。

方法 get_job 将像这样实现，尊重它的名字:

def get_job
  Job.find_by(id: params[:job_id])
end

Controller 中的用法是:

def destroy
  @job = get_job
  # etc.
end