Add missing timestamps to previously existing tables in Rails

add_timestamps_rails.rb

## rails g migration add_timestamps
## Insert the following, with whatever version of ActiveRecord you're using.

class AddTimestamps < ActiveRecord::Migration[5.0]
  def change
    ActiveRecord::Base.connection.tables.each do |table_name|
      columns = ActiveRecord::Base.connection.columns(table_name).map { |c| c.name }
      ["created_at", "updated_at"].each do |timestamp|
        unless columns.include?(timestamp)
          add_column table_name, timestamp, :datetime
        end
      end
    end
  end
end

## rake db:migrate

Note to anyone looking - this does not include the null: false option. I found that running it with that threw errors on the schema_migrations column. You may not even want schema_migrations to have timestamps, so feel free to skip that in the script if you want to include the null option. And if anyone knows why it behaves that way, I'm all ears!