Rake db:seed抱怨表单没有被多部分编码

我有一个seeds.rb文件:

activity1 = Activity.create! :name => 'Football', :icon => File.read("#{Rails.root}/public/images/activity_icons/football.png")

但是当我跑的时候 rake db:种子 ,进程失败,并收到错误消息:

You tried to assign a String or a Pathname to an uploader, for security reasons, this is not allowed.

If this is a file upload, please check that your upload form is multipart encoded.

好吧,手动图标上传确实有用,因为我的表单 是 多部分编码,所以我猜rake正在使用它自己的运行seeds.rb的表单。

我要做什么才能使这工作?除了每次重新创建数据库时手动添加图标之外