why it’s? Rails5.1 or later is Breaking Changed ActiveRecord Default Primary Keys to BIGINT on MySQL and PostgreSQL. here a reset the Default Primary Key to an INTEGER. Rails5.1 ReleaseNote Ruby on Rails 5.1 Release Notes - Ruby on Rails Guides
Edit descriptionguides.rubyonrails.org Change Default Primary Keys to BIGINT. (Pull Request) Change Default Primary Keys to BIGINT by jmccartie · Pull Request #26266 · rails/rails
Friends don't let friends use INT as a primary key. - Schneems (@schneems) May 13, 2016 Summary Per a conversation with…github.com