Rails - Jul 2008 - Polymorphic associations and forms

Hi,

I''ve got an issue where I''m creating a form in my view where
the user
can add a Sponsorship to an Event (m2m relationship using has_many
:through). A Sponsorship belongs to an event and also belongs to a
sponsor. The sponsor is a polymorphic relationship with either a Partner
or a Company. So I have these columns set up:

Event
  id
  name
  date

Sponsorship
  event_id
  sponsor_type
  sponsor_id

I created a view, much like in railscasts 3-part complex forms tutorial
where I can dynamically add and remove sponsorships for the event, and
there''s a <select> field for choosing whether the sponsorship is
for a
Partner or Company and then I have 2 more <select> fields, one with a
list of Partners and one with a list of Companies. I set up virtual
attributes in the Event model  for :company_id and :partner_id and I
have logic in that model as well which wires everything up the best I
can (because of the way this is working, I couldn''t figure out how to
make everything work like magic as in the railscast, but I did get that
working for a non-polymorphic relationship elsewhere in the project).

Everything saves fine, but when I render the view, the Company and
Partner <select> fields aren''t set to the proper values. This is
because
they''re set to use :partner_id and :company_id rather than :sponsor_id.

Is there any way of doing this? anyone know where I''m going wrong?

some sample code:

## the partial =>
<div class="sponsor">
<% fields_for ''event[sponsor_attributes][]'', sponsor do
|sf| -%>
  <fieldset>
    <legend>Sponsor</legend>
    <%= sf.select(:sponsor_type, @sponsor_types, { :prompt =>
''Select a
type...'' }, :index => nil )%>
    <div>
      <%= label_tag ''Candidate:'' %>
      <%= sf.select(:company_id, @companies, {:prompt => ''Choose
a
company...'' }, :index => nil ) %>
    </div>
    <div>
      <%= label_tag ''Partner: '' %>
      <%= sf.select(:partner_id, @partners, { :prompt => ''Choose
a
partner...'' }, :index => nil ) %>
    </div>

    <% if sponsor.new_record? -%>
      <%= link_to_function ''[-] Remove'',
"this.up(''.sponsor'').remove()"
%>
    <% else -%>
      <%= link_to_function ''[-] Remove'',
"mark_for_destroy(this,
''sponsor'')" %>
      <%= sf.hidden_field :id, :index => nil %>
      <%= sf.hidden_field :should_destroy, :index => nil, :class =>
''should_destroy'' %>
    <% end -%>
  </fieldset>
<% end -%>
</div>


## the Event model''s important stuff (yes, I know... this is a mess)
=>
  def sponsor_attributes=(sponsor_attributes)
    sponsor_attributes.each do |attrib|
      unless attrib[:sponsor_type].blank? # it''s just an empty field...
        if attrib[:id].blank? # it''s a new sponsorship!
          s = sponsorships.build()
        else # it''s an existing sponsorship
          s = sponsorships.detect { |sp| sp.id == attrib[:id].to_i }
        end

        s.sponsor_type = attrib[:sponsor_type]

        # load the correct sponsor_id
        case attrib[:sponsor_type]
        when ''Company''
          s.sponsor_id = attrib[:company_id]
        when ''Partner''
          s.sponsor_id = attrib[:partner_id]
        end
      end
    end
  end

If I missed anything, let me know.

Thanks in advance.


...spike
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