Generating an Instagram- or Youtube-like unguessable string ID in ruby/ActiveRecord

Question

Upon creating an instance of a given ActiveRecord model object, I need to generate a shortish (6-8 characters) unique string to use as an identifier in URLs, in the style of

Answer 1

You could do something like this:

random_attribute.rb

module RandomAttribute

  def generate_unique_random_base64(attribute, n)
    until random_is_unique?(attribute)
      self.send(:"#{attribute}=", random_base64(n))
    end
  end

  def generate_unique_random_hex(attribute, n)
    until random_is_unique?(attribute)
      self.send(:"#{attribute}=", SecureRandom.hex(n/2))
    end
  end

  private

  def random_is_unique?(attribute)
    val = self.send(:"#{attribute}")
    val && !self.class.send(:"find_by_#{attribute}", val)
  end

  def random_base64(n)
    val = base64_url
    val += base64_url while val.length < n
    val.slice(0..(n-1))
  end

  def base64_url
    SecureRandom.base64(60).downcase.gsub(/\W/, '')
  end
end
Raw

user.rb

class Post < ActiveRecord::Base

  include RandomAttribute
  before_validation :generate_key, on: :create

  private

  def generate_key
    generate_unique_random_hex(:key, 32)
  end
end