migration.rb

class AddRandomSlugToReports < ActiveRecord::Migration
  def self.up
    change_table :reports do |t|
      t.string :slug
      t.index :slug
    end
    Report.reset_column_information
    Report.all.each do |report|
      report.generate_slug!
      report.save
    end
  end
  
  def self.down
    change_table :reports do |t|
      t.remove :slug
      t.remove_index :slug
    end
  end
end

report.rb

class Report
  before_create :generate_slug!

  # There are a lot of ways to generate slugs. SecureRandom.hex is easy enough.
  # You need to test for uniqueness -- sometimes I'll use a loop counter as
  # the param for SecureRandom.hex, so we still get to favor short URLs
  # without worrying too much about collisions.
  
  # The only other change I might make to this would be to generate a
  # random slug from a different character set. For example, avoiding
  # phonetically or graphically similar characters.

  def generate_slug!
    unless slug.present?
      slug_size = 2
      self.slug = ActiveSupport::SecureRandom.hex(slug_size)
      while self.count(slug) > 0
        count = count + 1
        self.slug = ActiveSupport::SecureRandom.hex(slug_size)
      end
    end
  end
end