gistfile1.txt

class User < ActiveRecord::Base
  # Paperclip
  has_attached_file :photo,
     :styles => {
       :thumb=> "100x100#",
       :small  => "150x150>",
       :medium => "300x300>",
       :large =>   "400x400>" }


This is the method for where the user uploads the photo: 

  # normally we use all lowercase for methods just fyi:
  # ex:   def photo_upload   
  # 
  # Also, now this method needs to be submitted with a :id parameter:
  # so you'd have the form post to this URL:
  #
  # /your_controller/photoUpload/69
  # 
  # And this would send the photo up for user with id 69, see:
  #
  def photoUpload   
    @user = User.find(params[:id])
  end

And this is the view for uploading that photo: 

<%= error_messages_for :photo %>

<% form_for(@user,:html => { :multipart => true }) do |f| %>
<%= f.error_messages %>
 <p>
    <%= f.label 'Photo' %><br />
    <%= f.file_field :photo %>
  </p>
  <p>
    <%= submit_tag 'Upload' %>
  </p>
<% end -%>

# This form will generate a form field that will post to the 
# UserController, and will most likely be trying to create a user.  Why don't you use
# the normal form tag instead of trying to use the form_for -- it's only good
# for RESTful, straight up, CRUD operations (the basic create, read, update, delete actions).
#
# how about instead:

<%= error_messages_for :photo %>
<% form_tag("/users/photoUpload/#{@user.id}", :html => { :multipart => true }) do %>

 <p>
    <%= label_tag 'Photo' %><br />
    <%= file_field_tag 'photo' %>
  </p>
  <p>
    <%= submit_tag 'Upload' %>
  </p>
<% end -%>