Rails - Parameters not being saved when using nested forms in Cocoon - ruby-on-rails

Question

I've followed Cocoon's instructions for creating a nested form for a has_many association but there's one thing that I can't seem to figure out. I'm able to add an existing genre to my project but when it comes to creating a completely new one the parameters for my genres aren't being permitted. When I refer to my rails console to debug the issue this is the message I receive upon update:
Unpermitted parameters: genre_attributes
What's strange is I've permitted both my join table genreships and my genre model along with having my movie model accept their nested attributes but still no luck. There has to be something I'm not doing in my movie_params method but not able to find what. I've literally tried to permit every possible attribute within this method and completely out of ideas on what could be the solution
Models
class Movie < ActiveRecord::Base
has_many :genreships
has_many :genres, through: :genreships
accepts_nested_attributes_for :genres, :reject_if => :all_blank, :allow_destroy => true
accepts_nested_attributes_for :genreships, :reject_if => :all_blank, :allow_destroy => true
extend FriendlyId
friendly_id :title, use: :slugged
end
class Genreship < ActiveRecord::Base
belongs_to :movie
belongs_to :genre
accepts_nested_attributes_for :genre, :reject_if => :all_blank
end
class Genre < ActiveRecord::Base
has_many :genreships
has_many :movies, through: :genreships
extend FriendlyId
friendly_id :name, use: :slugged
end
Movies Controller
def movie_params
params.require(:movie).permit(:title, :release_date, :summary, genreships_attributes: [:id, :genre_id, :_destroy], genres_attributes: [:id, :_destroy, :name])
end
Form
= simple_form_for #movie do |f|
.field
= f.input :title
.field
= f.input :release_date, label: 'Release Date', order: [:month, :day, :year], start_year: 1901
.field
= f.input :summary, as: :text
#genres
= f.simple_fields_for :genreships do |genreship|
= render 'genreship_fields', :f => genreship
= link_to_add_association 'add a genre', f, :genreships
.actions = f.submit 'Save', class: 'btn btn-default'
Genreship Partial
.nested-fields
#genre_from_list
= f.association :genre, :collection => Genre.order(:name), :prompt => 'Choose an existing genre'
= link_to_add_association 'or create a new genre', f, :genre
= link_to_remove_association "remove genre", f
Genre Partial
.nested-fields
= f.input :name
Here's what's shown in the rails console right after posting a new movie:
Started POST "/movies" for 127.0.0.1 at 2014-11-19 08:17:42 -0500
Processing by MoviesController#create as HTML
Parameters: {"utf8"=>"✓", "authenticity_token"=>"2/wqXhn/x73AdOOrSo49Q/OPAmrcVk0rLViJJNpIhps=", "movie"=>{"title"=>"", "release_date(2i)"=>"11", "release_date(3i)"=>"19", "release_date(1i)"=>"2014", "summary"=>"", "genreships_attributes"=>{"1416403056574"=>{"genre_attributes"=>{"name"=>"Comedy"}, "genre_id"=>"", "_destroy"=>"false"}}}, "commit"=>"Save"}
Unpermitted parameters: genre_attributes

Answer 1

You use genre_attributes while genres_attributes (plural form) is defined in your controller. Change it to:
def movie_params
params.require(:movie).permit(:title, :release_date, :summary, genreships_attributes: [:id, :genre_id, :_destroy], genre_attributes: [:id, :_destroy, :name])
end

Answer 2

I created a solution that in a sense deviates from Nathan's example code somewhat but gets the job done nonetheless. Simply moving this line from genreship_fields.html.slim to _form.html.slim did the trick:
link_to_add_association 'create a new genre', f, :genres
My partials now look like this:
Form
= simple_form_for #movie do |f|
.field
= f.input :title
.field
= f.input :release_date, label: 'Release Date', order: [:month, :day, :year], start_year: 1901
.field
= f.input :summary, as: :text
#genres
= f.simple_fields_for :genreships do |genreship|
= render 'genreship_fields', :f => genreship
| #{link_to_add_association 'add a genre', f, :genreships} | #{link_to_add_association 'create a new genre', f, :genres}
.actions = f.submit 'Save', class: 'btn btn-default'
Genreship Partial
.nested-fields
#genre_from_list
= f.association :genre, :collection => Genre.order(:name), :prompt => 'Choose an existing genre'
= link_to_remove_association "remove genre", f
Genre Partial
.nested-fields
= f.input :name
= link_to_remove_association "remove form", f