Where do the created_at and updated_at columns come from?

Question

All the tables in the database created by a rails application seem to have created_at and updated_at columns. What creates these? Are they optional, or does something internal rely on them?

Answer 1

They are created by default when you run the ActiveRecord migration for a model. ActiveRecord automatically populates/updates them when you create or update a model instance (and thus the underlying database table row) respectively.

You can remove the columns by removing the t.timestamps line from within the model migration file.

• Ruby on Rails Guides: Migrations