Trying to validate two fields conditionally. If either video_url or video_title is not blank then the other must not be empty.

post.rb

require 'video_title_validator'

class Post < ActiveRecord::Base
  attr_accessible :body, :title, :image, :video_title, :video_url

  validates :video_url, :presence => true, :if => :video_title_blank?
  
  belongs_to :author, class_name: "User"
  has_many :comments
  has_many :parent_comments, class_name: "Comment", conditions: { parent_comment_id: nil }
  has_many :images
  mount_uploader :image, ImageUploader

end

video_title_validator

class VideoTitleValidator < ActiveModel::Validator

  def video_title_blank?(record)
    if record.video_title
      record.errors[:base] << "Video must have a title"
    end
  end
end