带有Carrierwave的条件版本/流程

def admin_upload?
  user.admin? && file.size > 1.megabyte
end

def store_dir
  if admin_upload?
    "uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
  else
    "public_uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
  end
end

def create
  @upload = Upload.new(upload_params)
  if @upload.admin_upload?
    if @upload.save
      redirect_to @upload, notice: 'Upload was successfully created.'
    else
      render :new
    end
  else
    flash[:alert] = 'You are not authorized to upload files larger than 1MB.'
    render :new
  end
end