UniqueIndexChecker

Imagine your model has a unique index in the database but doesn't have validates :email, uniqueness: true validation. In that case, you're sure that you won't have duplicated values in the database. But each attempt to save a duplicated value on that field will be rolled back with an error raised and without errors on your object. Mostly, you'd like to catch it properly and for that uniqueness-validator exists. This checker also supports a unique index on multiple columns (which should have a validates :email, uniqueness: { scope: :last_name } validation).