Rails 3 has_many :through form with dropdown menus? - ruby-on-rails

Question

I'm trying to implement a has_many :through join in Rails 3 (with Formtastic) and I'm a little stuck. I have the models set up as follows:
Models:
class Project < ActiveRecord::Base
has_many :employees, :through => :teams
has_many :teams
class Employee < ActiveRecord::Base
has_many :projects, :through => :teams
has_many :teams
class Team < ActiveRecord::Base
belongs_to :project
belongs_to :employee
And this line gives me a multi-select box in the projects view that allows employees to be selected:
View:
<%= f.input :employees, :as => :select %>
So far this gets the job done, but what I'd LIKE to have is a separate dropdown box to select each employee's name, then their role in the project. I can't figure out the form code to get me there...
EDIT:
As suggested, I've gotten the code from Railscast 197: Nested Model Forms working and it's part-way there. This is what I have in the view:
<%= f.semantic_fields_for :employees do |builder| %>
<%= render 'employee_fields', :f => builder %>
<% end %>
<%= link_to_add_fields "add employee", f, :employees %>
and the 'employee_fields' partial:
<p class="fields">
<%= f.input :name, :as => :select, :collection => Employee.find(:all) %>
<%= f.hidden_field :_destroy %>
<%= link_to_remove_fields "remove", f %>
</p>
But right now this creates a new employee rather than a new team (project-employee join record), so I think it's acting as a has_many rather than a has_many :through. How can I edit this so that the :name input above adds a record to project[employee_ids][]?

Answer 1

Oh my god, I finally got this thing to work. Here's the relevant code, minus the bits added to make the form add and remove fields dynamically:
_form.html.erb
<%= semantic_form_for #project do |f| %>
.
.
<%= f.semantic_fields_for :teams do |builder| %>
<input id="project_teams_none" name="team[employee_ids][]" type="hidden" value="" />
<%= render 'team_fields', :f => builder %>
<% end %>
_team_fields.html.erb
<div class="input">
<%= f.collection_select(:employee_id, Employee.all, :id, :name, :include_blank => true ) %>
</div>
The key was adding the <input id="project_teams_none" name="team[employee_ids][]" type="hidden" value="" /> line in manually, because for whatever reason this wasn't generated as part of the form. This got the form to actually start updating things, and then I just had to make the nested form refer to the join model (team) rather than to employees so that the updates were going to the right place.
Looks so simple now!