Rails - Jun 2011 - using collection_select with accepts_nested_attributes_for to generate many-to-many relations for an event invitation app

Hi,

New rails developer here trying to learn my way around active record
associations.

I''m building an event scheduling application and am working on the
invitation feature. I already have a basic when / where event creation
form and I now want to make a way for the event creator to generate a
list of users who are invitees to the event from a list of the
creator''s friends on the site (friends are recorded by a reflexive
has_many :through friendship relationship on the User model) . I have
set up a has_many :through invitation model to represent the many to
many relatiionship between events and users (invitees). The respective
models look like this:

User.rb

    class User < ActiveRecord::Base

          has_many :friendships
          has_many :friends, :through => :friendships

          attr_accessor :password
 
attr_accessible :first_name, :middle_name, :last_name, :email, :zipcode,
:password, :password_confirmation

          has_many :events

          has_many :invitations
          has_many :events, :through => :invitations

    end

Event.rb

    class Event < ActiveRecord::Base

 
attr_accessible :title, :description, :location, :time_start, :time_end,
:event_access_type

      belongs_to :user

      has_many :invitations
      has_many :invitees, :through => :invitations

      accepts_nested_attributes_for :invitations

    end

Friendship.rb

    class Friendship < ActiveRecord::Base

      belongs_to :user
      belongs_to :friend, :class_name => "User"

    end

Invitation.rb

    class Invitation < ActiveRecord::Base

      belongs_to :event
      belongs_to :invitee, :class_name => "User"

    end

What I''m trying to with the form is generate a drop down list with the
multiple selection enabled (terrible UI I know, but this is just for
testing and prototyping purposes) that is populated with the current
user''s friends on the site. In order to this I am currently using this
form helper method:

    <%= collection_select(:friendship, :friend_id,
current_user.friendships , :friend_id, :friends_name, {}, html_options
= {:multiple => true}) %>

this generates a drop down which I want to submit the friend_ids (i.e.
user_ids) of the users that the event creator wants to invite.  My
next step is to take these selections upon submission and use each of
the friend_id values to then generate a new invitation association
between the created event and the friend. My understanding is that
since this a multi-model form I''ll need to include
"accepts_nested_attributes_for :invitations" in the event model. My
basic problem is I''m not clear on what the form and controller syntax
should be to take the submitted drop down values and use them to
generate new invitation objects. Here is my latest attempt at the form
view:

_event.form.html.erb

    <%= form_for(@event) do |f| %>
      <%= render ''shared/error_messages'', :object =>
f.object %>
      <div class="field">
    	<%= f.label :title %><br />
    	<%= f.text_field :title %>
      </div>
      <div class="field">
    	<%= f.label :description %><br />
    	<%= f.text_area :description %>
      </div>
      <div class="field">
    	<%= f.label :location %><br />
    	<%= f.text_field :location %>
      </div>
      <div class="field">
        <%= f.label "Event type" %><br />
        <%= select( "event", "event_access_type",
{"" => "", "Public"
=> "public", "Friends of Friends" =>
"friends_of_friends", "Private
(Invite Only)" => "private"}) %>
      </div>
    	<% f.fields_for :invitation do |invitation_form| %>
    		<div class="field">
    			<%= invitation_form.label "Who''s invited?"
%><br />
    			<%= collection_select(:friendship, :friend_id,
current_user.friendships , :friend_id, :friends_name, {}, html_options
= {:multiple => true}) %>
    		</div>
    	<% end %>
      <div class="actions">
        <%= f.submit "Submit" %>
      </div>
    <% end %>

Would greatly appreciate it if someone could offer their guidance on
how this would be done and if I am making a many mistakes in terms of
the relations or form methods I am using.

Thanks!

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