Read the part "Concurrency and integrity" in the Rails documentation: http://apidock.com/rails/ActiveRecord/Validations/ClassMethods/validates_uniqueness_of htt

Read the part "Concurrency and integrity" in the Rails documentation: http://apidock.com/rails/ActiveRecord/Validations/ClassMethods/validates_uniqueness_of http://apidock.com/rails/ActiveRecord/Validations/ClassMetho... You need to enforce the uniqueness in the DB.