ruby-on-rails-4 – 为什么当我在rails 4中使用carrierwave上传

如果我不选择图像上传,只发送字符串,所有工作正常但如果我发送图像文件我得到这样的错误：

TypeError: can't cast ActionDispatch::Http::UploadedFile to string: INSERT INTO "items" ("created_at","description","image","name","store_id","sub_items","title","updated_at") VALUES (?,?,?)
   (0.2ms)  rollback transaction
*** ActiveRecord::StatementInvalid Exception: TypeError: can't cast ActionDispatch::Http::UploadedFile to string: INSERT INTO "items" ("created_at",?)

我的看法 ：

<%= form_for @items,:url => dashboard_create_items_path(@store.id),:html => {:multipart => true} do |f| %>
  <%= f.label :name,'Name' %>
  <%= f.text_field :name %><br />
  <%= f.label :title,'Title' %>
  <%= f.text_field :title %><br />
  <%= f.label :image,'Image' %>
   <%= f.file_field :image %><br />
  <%= f.label :description,'Description' %>
  <%= f.text_field :description %><br />
  <%= f.label :sub_items %><br>
  <%= f.select :sub_items,options_for_select([["true",true],["false",false]]),:selected => 'true' %><br />
  <%= f.submit %>
<% end %>

我的控制器：

def create_items    
    store = Store.find(params[:id])
    @items = store.items.create(item_params)

    if @items
      redirect_to dashboard_show_items_url(@items.id,store.id)
    else
      redirect_to dashboard_new_items_url
    end
  end

private

    def item_params
      params.require(:item).permit(:name,:title,:image,:description,:sub_items,:store_id)
    end

我什么时候错了请告诉我？谢谢你