Custom sentinel values

DISCLAIMER: I believe this is bad advice except for very specific conditions when using MySQL. I recommend against it unless you notice performance performance problems in your production dataset on your production database. - jhawthorn

Some (FIXME: which?) databases ignore null columns when it comes to resolving unique index constraints. This means unique constraints that involve nullable columns may be problematic. Instead of using NULL to represent a not-deleted row, you can pick a value that you want paranoia to mean not deleted. Note that you can/should now apply a NOT NULL constraint to your deleted_at column.

Per model:

# pick some value
acts_as_paranoid sentinel_value: DateTime.new(0)

or globally in a rails initializer, e.g. config/initializer/paranoia.rb

Paranoia.default_sentinel_value = DateTime.new(0)