Change the default primary key type in Rails

September 1, 2020

Rails had changed the default type of the primary key from int to big int when creating a new table - Change Default Primary Keys to BIGINT #26266, but unless you are working with a big set of records (bigger than 2^31) it’s a waste of resources.

You can control that in your migration by passing id: false to the create_table method and then adding a primary_key column with you desired type ex:

  create_table :exercises, id: false do |t|
    t.primary_key :id, :serial
    ...
  end

In this case we are going to replace the default big int with a serial which is PostgreSQL specific . Serial is the same as integer except that PostgreSQL will automatically generate and populate values into the SERIAL column. This is similar to AUTO_INCREMENT column in MySQL or AUTOINCREMENT column in SQLite.