```ruby
class ChangeStoryPermalinkColumn < ActiveRecord::Migration
  def up
    change_column :stories, :permalink, :text
  end
end
```

Add down migration for change_column type
user
```ruby
class ChangeStoryPermalinkColumn < ActiveRecord::Migration
  def up
    change_column :stories, :permalink, :text
  end

  def down
    change_column :stories, :permalink, :string
  end
end
```
assistant