form_tag versus form_for with :multipart => true

Consider the following two ways of doing forms, both with :multipart => true. Only the form_for will work properly when using attachment_fu

<code> <%= form_tag :action => 'create', :multipart => true %>   <%= file_field 'assignment', :uploaded_data %>   <%= submit_tag "Create" %> <%= end_form_tag %> </code>

HTML: <code> <form action="/assignment/create?multipart=true" method="post"> </code>

<code> <% form_for :assignment, :url => {:action => 'create'}, :html => {:multipart => true}) do |f| %>    <%= file_field :assignment, :uploaded_data %>   <%= submit_tag "Upload Assignment" %> <% end %> </code>

HTML:

<code> <form action="/assignment/create" enctype="multipart/form-data" method="post">    <input id="assignment_uploaded_data" name="assignment[uploaded_data]" size="30" type="file" />   <input name="commit" type="submit" value="Upload Assignment" /> </form> </code>

Only the second form works with attachment_fu. Why are these two translations incompatible? I would expect the enctype to be specified on the first form above.

Thanks for any feedback,

  Gordon

the :multipart specification goes into the options hash for the form_tag, such as the following:

<% form_tag({:action => 'settings'}, {:multipart => true, :class => "form-style2"} ) do -%> ... <% end %>