How to associate intermediary model's extra column with value from a form - ruby

Question

I have a many to many relationship between Plays and Users with the intermediary WorksOn.
class Play < ActiveRecord::Base
has_many :works_on
has_many :users, :through => :works_on
end
class User < ActiveRecord::Base
has_many :works_on
has_many :plays, :through => :works_on
end
#The WorksOn model also has a :student_role field
class WorksOn < ActiveRecord::Base
belongs_to :user, :foreign_key => 'user_id' #these columns were added via a migration
belongs_to :play, :foreign_key => 'play_id'
end
And in Play's form I have a checkbox to select users
<div class="field" id="checkbox-list">
<%= f.label "Cast and Crew"%> <br />
<%= collection_check_boxes(:user_id, :user_ids, #users, :id, :simple_to_s) %> #simple_to_s defined in Play's model. #users defined in play controller's 'show' form
</div>
In Play's controller I manually create the associations using the checkbox id's.
#...
def update
#grab user_id from params and then the user_ids values
works_on = params[:user_id]
works_on = works_on[:user_ids].select{|id|id.length!=0} #rails includes hidden empty string field for checkboxes, must filter it out by removing the 0 length string
WorksOn.where(:play_id=>#play.id).destroy_all #remove previous associations
works_on.each do |user_id|
WorksOn.create(:play_id=>#play.id, :student_role => "aaaaaaaaa",:user_id=>user_id) #create new associations to user
end
#other update stuff -> respond_to do |format| ...
end
#...
The controller currently works but I want to have a text field associated with each check box, and when the admin hits submit the :student_role field uses that value instead of "aaaaaaaaa". Any ideas on how to get this started?
Also, bonus question. Why is :user_id a part of params and not play_params?
Thanks so much!

Answer 1

This ended up being more simple than I expected!
Play's new form
<div class="col-md-6 field checkbox-list">
<%= f.label "Cast and Crew"%> <br />
<%= collection_check_boxes(:user_id, :user_ids, #users, :id, :simple_to_s) %>
</div>
<div class="col-md-6 field user-roles-text-list">
<%= f.label "Roles and Responsibilities (eg Actor: Hamlet)"%> <br />
<% #users.each do |user| %> #add a text field for each checkbox
<%= text_field_tag "user_role[#{user.id}]", nil, placeholder: user.simple_to_s %>
<% end %>
</div>
Play controller
def associate_play_with_users( params )
user_ids = params[:user_id] #grab user_id hash from params
user_roles = params[:user_role]
user_ids = user_ids[:user_ids] #select the :user_ids key's values from the hash
user_ids = user_ids.select{|id|id.length!=0}#rails includes hidden empty string field for checkboxes, must filter it out by removing the 0 length string
WorksOn.where(:play_id=>#play.id).destroy_all #remove previous associations
user_ids.each do |user_id|
WorksOn.create(:play_id=>#play.id, :student_role => user_roles[user_id],:user_id=>user_id) #create new associations to user
end
end
Parameters
Parameters: {"utf8"=>"✓", "authenticity_token"=>"+7rIGuD59ld5lQHfTtRY130TkGCNnnHm4GJfBQJkP3C0IKmz4YStDxOcuxc2pKsS8nodB/UV1fR5XwWNXXbJ4w==",
"play"=>{"title"=>"As You Like It", "description"=>"a dope play faaao sho", "date_of_play(1i)"=>"3000", "date_of_play(2i)"=>"2", "date_of_play(3i)"=>"2", "date_of_play(4i)"=>"00", "date_of_play(5i)"=>"00"},
"user_id"=>{"user_ids"=>["69", "70", ""]},
"user_role"=>{"69"=>"ss", "70"=>"sssasasasas", "71"=>"", "72"=>"", "73"=>"", "74"=>""}, #only the ids from user_id are used, 69 and 70
"commit"=>"Update Play", "id"=>"17"}