Rails 4, Strong Parameters, and Nested Forms

_form.html.haml

= form_for @album do |f|
  = f.text_field :title
  = f.fields_for :songs do |s|
    = s.text_field :name
  ...

album.rb

class Album < ActiveRecord::Base
  has_many :songs
  accepts_nested_attributes_for :songs, allow_destroy: true
  ...
end

albums_controller.rb

class AlbumsController < ApplicationController
  ...
  private
   def album_params
        params.require(:album).permit(:title, songs_attributes: [:id, :_destroy, :name])
   end
end

song.rb

class Song < ActiveRecord::Base
  belongs_to :album
  ...
end