has and belongs to many magic

example.rb

class User < ActiveRecord::Base
  #magically looks up repertoires with user_id = this user's id
  has_many :repertoires
end

class Repertoire < ActiveRecord::Base
  #songly data and methods
  #requires user_id integer on repertoire table
  belongs_to :user
end

#add repertoire to user
user = User.find(x)
user.repertoires << Repertoire.create(params)

#find repertoires
user.repertoires 
user.repertoires.find(repertoire_id)
user.repertoires.where(song_name_field_thing: "Gangnam Style")

RepertoiresController < ActionController::Base
  def create
    repertoire = Repertoire.new(params[:repertoire])
    repertoire.user = current_user
    repertoire.save
  end
  
  def show
  #...
  end
  
  def update
  #...
  end
  
  def destroy
  #...
  end
  
  def edit
  #...
  end
end