Question

该应用程序的目标是方便用户上传/下载文件。

如果用户未选择任何文件并尝试点击上传，则需要显示提示。

def create
        @user = User.find(params[:user_id])
        @attachment = Attachment.new(params[:attachment => {:file => [ :original_filename ]}])

        if params[:attachment].nil?
          flash[:alert] = "No file!"
          render "new"
        end

        uploaded_io = params[:attachment][:file]
        @attachment.user_id = @user.id
        @attachment.name = params[:attachment][:file].original_filename
        @attachment.format = params[:attachment][:file].content_type
        @attachment.save
        File.open(Rails.root.join('public/data', @attachment.name), 'wb') do |file|
          file.write(uploaded_io.read)
        end

    redirect_to user_attachments_path, notice: "The file #{@attachment.name} has been uploaded."
end

尽管有if params[:atttachment].nil?阻止，但我在uploaded_io = params[:attachment][:file]语句中收到错误。

未选择任何文件时，

params[:attachment].nil?会返回true [使用调试器检查]

if块未执行的原因是什么？

Answer 1

你只有一个if循环，所以不管代码是否进入if循环，你都在执行if循环之外的每个代码，如果是else你需要处理它。这意味着代码之后如果循环将始终执行，如果它依赖于params[:attachment] 则不应该这样 我已使用正确的if else循环..更新了您的代码...

            def create
                @user = User.find(params[:user_id])
                @attachment = Attachment.new(params[:attachment => {:file => [ :original_filename ]}])
                ##you can use .blank?  as well
                if params[:attachment].nil?
                  flash[:alert] = "No file!"
                  render "new"
                else    
                 uploaded_io = params[:attachment][:file]
                 @attachment.user_id = @user.id
                 @attachment.name = params[:attachment][:file].original_filename
                 @attachment.format = params[:attachment][:file].content_type
                 @attachment.save
                 File.open(Rails.root.join('public/data', @attachment.name), 'wb') do |file|
                 file.write(uploaded_io.read)
                 end
                 redirect_to user_attachments_path, notice: "The file #{@attachment.name} has been uploaded."
               end
            end

Answer 2

你需要返回才能渲染，否则你会得到双重渲染错误，试试这样的事情

if params[:attachment].nil?
  flash[:alert] = "No file!"
  return render "new"
end

另外另一个注意事项是，当你直接渲染时，flash消息不会出现，它出现在下面的请求中，而是你需要告诉rails你希望那个flash消息立刻出现，所以不要只是使用flash，使用flash.now

if params[:attachment].nil?
  flash.now[:alert] = "No file!"
  return render "new"
end

尽管调用`render`，函数仍会执行

2 个答案: