models.rb

class Dog < ActiveRecord::Base
  has_many :videos
  has_many :photos
  belongs_to :user
end

class Video < ActiveRecord::Base
  has_many :dogs
  belongs_to :user
end

class Photo < ActiveRecord::Base
  has_many :dogs
  belongs_to :user
end

class User < ActiveRecord::Base
  has_many :dogs
  has_many :videos
  has_many :photo
end