roob.rb

class Controller
  def self.create_friend_request(user, params)
    obj = Model.new(params)
    if obj.valid?
      render json: obj, status: :created
    else
      render json: obj.errors, status: 400
    end

    unless Rails.env.development? || Rails.env.test?
      username = user.name
      friend = User.find params[:reciever_id]
      RpushService.send_notifications(friend, "New friend request from #{username}",
                                      {notification_type: 1})
    end
    return {json: "", status: 201}
  end
end

class Model
  validate :cannot_friend_self, on: :create
  validate :should_be_unique, on: :create

  private
  def cannot_friend_self
    count = self.class.count("sender_id=? and receiver_id=?", user.id, friend.id)
    errors.add(:user_id, "Cannot friend self") if count > 0
  end

  def should_be_unique
    count = self.class.count("sender_id=? and receiver_id=?", user.id, friend.id)
    errors.add(:some_other_id, "Users already friends") if count > 0
  end
end