Add missing created_at and updated_at columns in Rails

If, like me, you forgot to add the t.timestamps when creating a new table, you may want to add them in the future, however, most likely you already have data there.

To add those columns you can create a new migration and run this code in the change method

add_timestamps(:table_name)

This may work if you don't have data, but if you already have rows in your table you want to add a default value, one option is do do

add_timestamps(:notifications, default: DateTime.now)

The problem with this is that you are now storing the datetime value in your databaoption thisas a fixed value, so new rows will use this fixed value, to solve this problem change it to:

add_timestamps(:notifications, default: -> { "CURRENT_TIMESTAMP" })

This way it will work correctly and for already existent row it will use the timestamp of when you run the migration.