How to validate uniqueness only if value exists

I’m looking for the best way to use validation to confirm that an
optional field (hostname) is unique only if a value is entered in the

I was originally following the path shown in Agile Web D. with
Rails first edition, page 66, to define the “validate” method, but
didn’t have a clue how to include a uniqueness test there. Right now, I
have the following and it seems to be working as intended:

validates_uniqueness_of :hostname, :if => :hostname?

I guess I’m looking for some validation myself that this is a good way
to handle this. I’d also love to hear of other ways to make this work.



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