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


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:


    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



    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



    class Friendship < ActiveRecord::Base

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



    class Invitation < ActiveRecord::Base

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


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:


    <%= 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.