datamapper/dm-validations — pull request #69 by fsaravia (2013-12-03 16:16:42+00:00)
Title: Do not call validators if model is not dirty

There is no need to call validators (specially those which need to hit the database like :unique) if the model is not dirty.
This has special incidence, when a model has many parents with unique properties, in which the current version will call all validators for all parent models despite the fact that they don't need saving