Whenever you create a table from a database migration, remember to add updated_at and created_at timestamps to that table. Without those timestamps, investigating future bug reports will be hell. Always have timestamps.

Adding timestamps to new tables

Do you need DevOps-experts?

Your development team has a full backlog? No time for infrastructure architecture? Our DevOps team is ready to support you!

• We build reliable cloud solutions with Infrastructure as code
• We are experts in security, Linux and databases
• We support your dev team to perform

Read more Show archive.org snapshot

When you create a table using create_table, you can add timestamps by using the timestamps shortcut:

class CreateEpisode < ActiveRecord::Migration
  def change
    create_table :episodes do |t|
      t.string :name
      t.timestamps
    end
  end
end

ActiveRecord will automagically set those timestamps when you create or update a record.

Adding timestamps to existing tables

If you forgot to add timestamps in the past, take a look at your db/schema.rb and add timetamps for any table that is missing them. You can use the add_timestamps macros for that.

Rails >= 4.2

Since Rails 4.2 add_timestamps also adds a NOT NULL constraint by default. So you will see an error like "ERROR: column "created_at" contains null values" when you don't take care of it. Here are two approaches on how to handle this:

(a) Don't have a NOT NULL constraint:

class AddMissingTimestamps < ActiveRecord::Migration
  def change
    add_timestamps :shows, null: true
    add_timestamps :tags, null: true
    add_timestamps :users, null: true
  end
end

(b) Fill the datetimes with an old time (to mark it as being backfilled):

class AddMissingTimestamps < ActiveRecord::Migration
  def change
    # Add timestamps column, but without a NOT NULL constraint
    add_timestamps :shows, null: true

    # Backfill missing data with a really old date
    time = Time.zone.parse('2000-01-01 00:00:00')
    update "UPDATE shows SET created_at = '#{time}'"
    update "UPDATE shows SET updated_at = '#{time}'"

    # Restore NOT NULL constraints to be in line with the Rails default
    change_column_null :shows, :created_at, false
    change_column_null :shows, :updated_at, false
    
    # ...
  end
end

Rails < 4.2

class AddMissingTimestamps < ActiveRecord::Migration
  def change
    add_timestamps :shows
    add_timestamps :tags
    add_timestamps :users
  end
end

Also

Always have timestamps.