How to use long id in Rails applications?

If anyone needs this to work with PostgreSQL, create an initializer like this:

# config/initializers/bigint_primary_keys.rb
ActiveRecord::Base.establish_connection
ActiveRecord::ConnectionAdapters::PostgreSQLAdapter::NATIVE_DATABASE_TYPES[:primary_key] = 'bigserial primary key'

Because of lazy loading in Rails 3.2 (and maybe even earlier versions), ActiveRecord::ConnectionAdapters::PostgreSQLAdapter won't be required until you establish the database connection.