As you most likely know validates_uniqness_of :foreign_id does not allow nil values by default.

Rails professionals since 2007

Our laser focus on a single technology has made us a leader in this space. Need help?

• We build a solid first version of your product
• We train your development team
• We rescue your project in trouble

Read more Show archive.org snapshot

To allow nil one has to set the :allow_nil => true option.

Very unexpected scoping this validation will not raise an error if foreign_id set to nil for the first created record of this kind.

validates_uniqueness_of :foreign_id, :scope => :another_column # allows foreign_id to be nil

Without a validation for presence of foreign_id now unusual records could be created.