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 can hash the id:

Digest::MD5.hexdigest('1')[0..9]
=> "c4ca4238a0"
Digest::MD5.hexdigest('2')[0..9]
=> "c81e728d9d"

But somebody can still guess what you're doing and iterate that way. It's probably better to hash on the content