ujh/fountainpencompanion

class Friendship < ApplicationRecord
  belongs_to :friend, class_name: "User"
  belongs_to :sender, class_name: "User"

  validates :friend, uniqueness: { scope: :sender_id }
  validate :no_duplicate_requests
  validate :two_users

  private

  def no_duplicate_requests
    if self.class.find_by(sender: friend, friend: sender)
      errors.add(:friend, "Friend already sent request")
    end
  end

  def two_users
    errors.add(:friend, "You cannot friend yourself") if sender == friend
  end
end