file upload ...

i cant able to insert filename into database...pl;s help

my

model.rb
class Mobile < ActiveRecord::Base
validates_presence_of:image

validates_presence_of:brand
  def mobile=(picture_field)
    self.image = picture_field['image'].respond_to?(:original_filename)
? base_part_of(picture_field.original_filename) : nil

  end
def self.save(product)
  name=product['image'].original_filename
path = File.join("public/data", name)
File.open(path, "wb") { |f| f.write(product['image'].read) }

end
end
.........................................................
  controller.rb

def create
@mobile=Mobile.new(params[:mobile])
if @mobile.save
post=Mobile.save(params[:mobile])
redirect_to :action=>'list'
else
render :action=>'new'
end
end
...........................................

new.rhtml

<%= error_messages_for 'mobile' %>
<% form_tag ({ :action => 'create' },
              { :multipart => 'true' }) do%>
<p><%=text_field 'mobile','brand'%></p>
<p><%=file_field 'mobile','image'%></p>
<p><%=submit_tag 'Submit'%></p>
<%end%>