In Rails how would one generate a unique serial number for a new instance of a model?

问题

In Rails, I'm looking for a way to generate an auto-incrementing serial number for internal record keeping for new instances of a model. I would like to avoid creating database specific code and rather have a solution that will work regardless of the database. My current idea is to wait until the model is saved and then grab the ID of the saved model and use that as a suffix of the serial number, but then I would have to save each record twice on creation.

Any ideas?

Thanks for looking!

回答1:

I would recommend constructing the serial model in the model instead. This will give you more flexibility to adjust the serial number format later, and it will keep the unique auto-increment in the database instead. Use a regular auto-increment integer primary key and then create the serial number like this:

class Product
  def serial_number
    "PLN-%.6d" % id
  end
end

So if you have a product with id = 567 for example, you'll have a serial number like this:

Product.find(567).serial_number
=> PLN-000567

来源：https://stackoverflow.com/questions/5569391/in-rails-how-would-one-generate-a-unique-serial-number-for-a-new-instance-of-a-m