image uploadin error

hi all!
I m trying to upload image using paperclip in rails3…

In users controller of my application
(M TRYIN TO DISPLAY THE IMAGE IN THE SAME PAGE OF UPLOAD FILE(BUTTON) PAGE )
i ve defined 2 methods
def photo
end

def update_photo
end

** In photo.html.erb**
<%= image_tag @user.avatar.url(:medium) %>
<%= button_to “Delete”, user, :method => :delete, :confirm => ‘Are you sure to delete the image’ %>
<% form_for :user, @user, :url => update_photo_user_path(current_user), :html => { :multipart => true } do |form| %>






WEN I RUN DIS CODE IN THE BROWSER I GET

undefined method `avatar' for nil:NilClass ERROR

choose:
<%= form.file_field :avatar %>

<%= submit_tag(“Uploadfile”) %>

Hi,
In user model, do u have any field named avatar? and also y ur passing user as symbol and instance variable in form_for tag? remove the symbol.

Thanks,
Manivannan.s