Ruby on Rails: Can't mass-assign protected attributes

Question

Searched through all other same questions, nothing worked. I have User, which can create Track, but can also learn other Tracks. Learning other Tracks is saved in track_users.

model User.rb:

# has track as author!
has_many :tracks     
# has track as student!
has_many :tracks_users
has_many :courses, through: :tracks_users, source: :track
accepts_nested_attributes_for :tracks_users

model Track.rb

# has coach!
belongs_to :user
# has students!
has_many :tracks_users
has_many :students, through: :tracks_users, source: :user
accepts_nested_attributes_for :tracks_users

and model TracksUser.rb:

  attr_accessible :track_id, :user_id, :as => [:default, :admin]
  belongs_to :track
  belongs_to :user
  accepts_nested_attributes_for :track

and in my tracks/_follow.html.erb:

<%= form_for(current_user.courses.build(track_id: @track)) do |f| %>
    <div><%= f.hidden_field :track_id %></div>
    <%= f.submit "Take track", class: "btn btn-large btn-primary" %>
<% end %>

And this throws "Can't mass-assign protected attributes: track_id". I even set config.active_record.whitelist_attributes = false - doesn't work.

Answer 1

There is separate configuration option, explicitly for development stage - in config/environments/development.rb:

# Raise exception on mass assignment protection for Active Record models
config.active_record.mass_assignment_sanitizer = :strict

Error is gone by outcommenting that.

I have not seen this configuration mentioned anywhere in StackOverflow. Found it on http://net.tutsplus.com/tutorials/ruby/mass-assignment-rails-and-you/, so thanks tutsplus.