为什么在没有时间戳的情况下创建created_at / updated_at？

Question

I'm using rails 3.2 with the following migration and created_at/updated_at both get generated. I was under the impression that adding t.timestamps was what caused those columns to get generated.

class CreateContactsCountries < ActiveRecord::Migration
  def change
    create_table :contacts_countries do |t|
      t.string :name, :official_name, :null => false
      t.string :alpha_2_code, :null => false, :limit => 2
      t.string :alpha_3_code, :null => false, :limit => 3
    end

    add_index :contacts_countries, :alpha_2_code
  end
end

Answer 1

Please delete the table and check again becuase

By default, the generated migration will include t.timestamps (which creates 
the updated_at and created_at columns that are automatically populated 
by Active Record).

Ref this