A migration to add unique constraint to a combination of columns
According to howmanyofme.com, "There are 46,427 people named John Smith" in the United States alone. That's about 127 years of days. As this is well over the average lifespan of a human being, this means that a DOB clash is mathematically certain.
All I'm saying is that that particular combination of unique fields could lead to extreme user/customer frustration in future.
Consider something that's actually unique, like a national identification number, if appropriate.
(I realise I'm very late to the party with this one, but it could help future readers.)
You may want to add a constraint without an index. This will depend on what database you're using. Below is sample migration code for Postgres. (tracking_number, carrier)
is a list of the columns you want to use for the constraint.
class AddUniqeConstraintToShipments < ActiveRecord::Migration def up execute <<-SQL alter table shipments add constraint shipment_tracking_number unique (tracking_number, carrier); SQL end def down execute <<-SQL alter table shipments drop constraint if exists shipment_tracking_number; SQL endend
There are different constraints you can add. Read the docs