favorite.rb

# UserVideo
#  reference :user
#  reference :video
#  boolean :favorite
class UserVideo < ActiveRecord::Base
  belongs_to :user
  belongs_to :video
end

class Video < ActiveRecord::Base
end

class User < ActiveRecord::Base
  has_many :user_videos
  has_many :videos, :through => :user_videos
end

# recupere une video
video = Video.last

# cree une association
user.user_videos.create(video: video, favorite: true) # ou false

# choppe que les videos favorites
user.videos.where(user_videos: { favorite: true })

# change une video en favorite
user.user_videos.where(video: video).update(favorite: true)