Say in my schema I have a users table with an attribute field of pets that's default to ["dogs"]: 

```
create_table "users", force: true do |t|
    ...
    t.text    "pets",     default: ["dogs"],    array: true
    ...

```

I have a model `FriendlyUser` that inherits from class `User`: `class FriendlyUser < User`

Thus, when a `FriendlyUser` is created, the type is "FriendlyUser". But I would like `FriendlyUser` to have pets set to a default of dogs AND cats: ["dogs", "cats"] 

Is this possible with a migration, or must this be done in the class (by overriding an `initialize` method, using `after_initialize`, `before_create`, etc)?