add user cant follow himself validation

app/models/user_follow.rb

@@ -1,4 +1,12 @@
 class UserFollow < ApplicationRecord
   belongs_to :follower, class_name: 'User'
   belongs_to :followed, class_name: 'User'
+
+  validate :followed, :user_cant_follow_himself
+
+  private
+
+  def user_cant_follow_himself
+    errors.add(:followed, 'can\'t follow himself') if follower_id == followed_id
+  end
 end