many to many association mass assign checkboxes ruby on rails 4 - ruby-on-rails-4

Question

what i want to accomplish it's almost exactly the same as this!
railscast tutorial but can't get it to work.I have a courses table and a enrollments table they have a many to many relation so i have a join table called "courses_enrollments" i'd like to be able to add many courses to enrollments all at once from a form... i used a has_many_through relation and looped through all the courses in the form and for each of them i have a checkbox so i can add them to enrollments but when i save nothing happens my join table (courses_enrollments) never gets filled with the relations i want.... here are my models:
courses:
class Course < ActiveRecord::Base
has_many :courses_enrollments
has_many :enrollments, :through => :courses_enrollments
enrollments:
class Enrollment < ActiveRecord::Base
has_many :courses_enrollments
has_many :courses, :through => :courses_enrollments
and courses_enrollments:
class CoursesEnrollment < ActiveRecord::Base
belongs_to :courses
belongs_to :enrollments
end
and finally my enrollments form view:
<%= form_for(#enrollment) do |f| %>
<% if #enrollment.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(#enrollment.errors.count, "error") %> prohibited this enrollment from being saved:</h2>
<ul>
<% #enrollment.errors.full_messages.each do |message| %>
<li><%= message %></li>
<% end %>
</ul>
</div>
<% end %>
<div class="field">
<%= f.label :name %><br>
<%= f.text_field :name %>
</div>
<div class="field">
<%= f.label :state %><br>
<%= f.collection_select(:state, Courses.all, :id, :name, {:include_blank => true}, {:multiple => false}) %>
</div>
I also tried it like this in the form.... but nothing gets saved here either
<% Courses.all.each do |course|%>
<%= check_box_tag "enrollment[course_id][]", course.id %>
<%= course.name %>
<% end %>
</div>
<div class="actions">
<%= f.submit %>
</div>
<% end %>
i want to be able to save many records to the join table that holds the relation between the enrollments i am creating or updating and the courses i selected with the has many through association.... appreciate the help

Answer 1

Models:
class Course < ActiveRecord::Base
has_and_belongs_to_many :enrollments
class Enrollment < ActiveRecord::Base
has_and_belongs_to_many :courses
with this type of association you end up with a join table which will have course_id and enrollment_id . Thus not needing to create a new model just to handle your association. Rails already does that for you.
After that, in your controllers, make sure the accepted_params have this:
Controllers:
def course_params
params.require(:course).permit(
...
enrollments_ids: []
def enrollment_params
params.require(:enrollment).permit(
...
courses_ids: []