Update one column to value of another in Rails migration

I would create a migration

rails g migration set_updated_at_values

and inside it write something like:

class SetUpdatedAt < ActiveRecord::Migration
  def self.up
    Yourmodel.update_all("updated_at=created_at")
  end

  def self.down
  end
end

This way you achieve two things

• this is a repeatable process, with each possible deploy (where needed) it is executed
• this is efficient. I can’t think of a more rubyesque solution (that is as efficient).

Note: you could also run raw sql inside a migration, if the query gets too hard to write using activerecord. Just write the following:

Yourmodel.connection.execute("update your_models set ... <complicated query> ...")