CODEWITHSUNDEEP
rubyuuiduniqueidentifier
Derick Bailey
Derick Bailey

Reputation: 72858

Ruby UUID and uniqueness, for an ID

I need a 6 character alphanumeric ID for use in my rails app, which will be presented to users of the system and must be unique among all the object instances in my system. I don't expect more than a few thousand object instances, so 6 characters is far more than I really need.

At this point I'm using the UUIDTools gem in my Rails app to generate a uuid. Which of the UUIDTools generation methods should I use, and which end of the resulting uuid should I take the 6 characters from, to guarantee uniqueness?

for example, if I generate ef1cf087-95c9-4868-bd95-cea950a52b58, would I want to use ef1cf0 from the front of it, or a52b58 from the back end?

... as a side note / question: am i going about this wrong? is there a better way?

Upvotes: 0

Views: 2831

Answers (2)

Mark Westling
Mark Westling

Reputation: 5974

When you say that incrementing the ID isn't an option, is that because you don't want users to see the scheme you're using, or because the generation must be stateless (i.e., you can't keep track of all IDs you've generated)?

If it's the former, then you can generate an ID, check to see if you've already used it, and if so, generate another new ID. (Seems pretty obvious so sorry if I'm on the wrong track.) You could do something like this:

while id = rand(2**256).to_s(36)[0..5] 
   break unless Ids.exists?(id)
end

where Ids.exists?(id) is the does-this-already-exist method.

Upvotes: 3

Andrey
Andrey

Reputation: 60105

No way. UUID is considered unique because it is very long and it is practically impossible to generate same UUIDs. If you trim it to 6 chars then you drammatically increase possiblility of duplicate. You have to use either incrementing id or full UUID.

Only deterministic generation (id(x + 1) = id(x) + 1) can guarantee uniqueness. UUID doesn't guarantee it and 6 chars guarantee it even less.

Other option is to create ID generation service, it will have single method getNewId and will keep knowledge that will be enought to provide unique ids. (Simplest case - counter)

Upvotes: 6

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