Nested form using paperclip - ruby-on-rails

Question

I have a model called posts, and it has many attachments.
The attachments model is using paperclip.
I made a standalone model for creating attachments which works just fine, this is the view as instructed here (https://github.com/thoughtbot/paperclip):
<% form_for :attachment, #attachment, :url => #attachment, :html => { :multipart => true } do |form| %>
<%= form.file_field :pclip %>
<%= form.submit %>
<% end %>
The nested form in posts looks like this:
<% #attachment = #posts.attachments.build %>
<%= form_for(#posts) do |f| %>
<% if #posts.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(#posts.errors.count, "error") %> prohibited this post from being saved:</h2>
<ul>
<% #posts.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>
<% end %>
<div class="field">
<%= f.label :name %><br />
<%= f.text_field :name %>
</div>
<div class="field">
<%= f.label :description %><br />
<%= f.text_area :description %>
</div>
<div class="field">
<%= f.fields_for :attachments, #attachment, :url => #attachment, :html => { :multipart => true } do |at_form| %>
<%= at_form.file_field :pclip %>
<% end %>
</div>
<div class="actions">
<%= f.submit %>
</div>
<% end %>
An attachment record is created, but its empty. The file is not uploaded. The post meanwhile, is successfully created...
Any ideas?

Answer 1

You are missing the :multipart option in your form definition:
<% #attachment = #post.attachments.build %>
<%= form_for #post, :html => { :multipart => true } do |f| %>
<% if #post.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(#post.errors.count, "error") %> prohibited this post from being saved:</h2>
<ul>
<% #post.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>
<% end %>
<div class="field">
<%= f.label :name %><br />
<%= f.text_field :name %>
</div>
<div class="field">
<%= f.label :description %><br />
<%= f.text_area :description %>
</div>
<div class="field">
<%= f.fields_for :attachments, #attachment do |at_form| %>
<%= at_form.file_field :pclip %>
<% end %>
</div>
<div class="actions">
<%= f.submit %>
</div>
<% end %>
Also, your #posts variable should really be #post (single ActiveRecord instance as opposed to an array of ActiveRecord instances).