app/models/user.rb
class User < ActiveRecord::Base
devise :database_authenticatable, :registerable,
:recoverable, :rememberable, :trackable, :validatable
has_many :photos, dependent: :destroy
has_many :comments, dependent: :destroy
has_many :likes, dependent: :destroy
has_many :commented_photos, through: :comments, source: :photo
has_many :liked_photos, through: :likes, source: :photo
end