Rails: change column type, but keep data

A standard migration using the change_column method will convert integers to strings without any data loss. rake db:rollback will also do the reverse migration without error if required.

Here is the test migration I used to confirm this behaviour:

class ChangeAgeToString < ActiveRecord::Migration
  def self.up
    change_column :users, :age, :string
  end

  def self.down
    change_column :users, :age, :integer
  end
end