How do I auto-increment a unique version number using ActiveRecord?

Question

I have a model License that needs to have a version number (an Integer) but I don't want that to be confused at all with the actual id.

I have a field version_number. What is the simplest way to tell ActiveRecord to automatically increment it on creation?

How thread-safe does this need to be? We've found that with multiple Rails processes running over multiple servers, the only way to generate truly unique version numbers was to delegate the generation to an external service; in our case using a Postgres sequence. — Graham Savage, Oct 01 '11 at 07:17

score 1 · Accepted Answer · answered Sep 27 '11 at 04:05

1

Use a before_create callback to set version_number to the last version + 1:

class License < ActiveRecord::Base
  before_create :set_version
  ...
  def set_version
    license = License.last
    current_version = license.nil? ? 0 : license.version_number
    self.version_number = current_version + 1
  end
  ...
end

answered Sep 27 '11 at 04:05

Adam Eberlin

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To get the next version you could also do `self.version_number = ( License.maximum(:version_number) || 0 ) + 1` – DanneManne Sep 27 '11 at 04:21
Thanks Adam and nice one Danne. That does exactly what I am after. – Dave Sag Sep 27 '11 at 08:42

How do I auto-increment a unique version number using ActiveRecord?

1 Answers1