Best way to create unique token in Rails?

Question

-- Update --

As of January 9th, 2015. the solution is now implemented in Rails 5 ActiveRecord's secure token implementation.

-- Rails 4 & 3 --

Just for future reference, creating safe random token and ensuring it's uniqueness for the model (when using Ruby 1.9 and ActiveRecord):

class ModelName < ActiveRecord::Base

  before_create :generate_token

  protected

  def generate_token
    self.token = loop do
      random_token = SecureRandom.urlsafe_base64(nil, false)
      break random_token unless ModelName.exists?(token: random_token)
    end
  end

end

Edit:

@kain suggested, and I agreed, to replace begin...end..while with loop do...break unless...end in this answer because previous implementation might get removed in the future.

Edit 2:

With Rails 4 and concerns, I would recommend moving this to concern.

# app/models/model_name.rb
class ModelName < ActiveRecord::Base
  include Tokenable
end

# app/models/concerns/tokenable.rb
module Tokenable
  extend ActiveSupport::Concern

  included do
    before_create :generate_token
  end

  protected

  def generate_token
    self.token = loop do
      random_token = SecureRandom.urlsafe_base64(nil, false)
      break random_token unless self.class.exists?(token: random_token)
    end
  end
end

Ryan Bates uses a nice little bit of code in his Railscast on beta invitations. This produces a 40 character alphanumeric string.

Digest::SHA1.hexdigest([Time.now, rand].join)

This might be a late response but in order to avoid using a loop you can also call the method recursively. It looks and feels slightly cleaner to me.

class ModelName < ActiveRecord::Base

  before_create :generate_token

  protected

  def generate_token
    self.token = SecureRandom.urlsafe_base64
    generate_token if ModelName.exists?(token: self.token)
  end

end

There are some pretty slick ways of doing this demonstrated in this article:

https://web.archive.org/web/20121026000606/http://blog.logeek.fr/2009/7/2/creating-small-unique-tokens-in-ruby

My favorite listed is this:

rand(36**8).to_s(36)
=> "uur0cj2h"

If you want something that will be unique you can use something like this:

string = (Digest::MD5.hexdigest "#{ActiveSupport::SecureRandom.hex(10)}-#{DateTime.now.to_s}")

however this will generate string of 32 characters.

There is however other way:

require 'base64'

def after_create
update_attributes!(:token => Base64::encode64(id.to_s))
end

for example for id like 10000, generated token would be like "MTAwMDA=" (and you can easily decode it for id, just make

Base64::decode64(string)

This may be helpful :

SecureRandom.base64(15).tr('+/=', '0aZ')

If you want to remove any special character than put in first argument '+/=' and any character put in second argument '0aZ' and 15 is the length here .

And if you want to remove the extra spaces and new line character than add the things like :

SecureRandom.base64(15).tr('+/=', '0aZ').strip.delete("\n")

Hope this will help to anybody.