class Relationship < ActiveRecord::Base belongs_to :follower, class_name: "User" belongs_to :following, class_name: "User" validates :follower_id, presence: true validates :following_id, presence: true end class User < ActiveRecord::Base # 省略 has_many :following_relationships, foreign_key: "follower_id", class_name: "Relationship", dependent: :destroy has_many :followings, through: :following_rela