How can I customize only a field in rails_admin?

I have a field for which rails_admin generates a textfield, but I'd like it to use a <select> tag instead. I customized the field like this, in my initializer:

RailsAdmin.config do |config|
  config.model User do
    update do
      field :state do
        partial "user_state_partial"
      end
    end
  end
end

I've tested it, and it works. The problem is, by doing like this ( I tried with an edit block too ), the only field left, is the one I'm customizing. Is there any way of telling rails_admin to just assume the defaults for the other fields?

Once you have defined one field, you have to define all fields that you want to use. The default is all fields.

RailsAdmin.config do |config|
  config.model User do
    update do
      field :name
      field :surname
      field :state do
        partial "user_state_partial"
      end
    end
  end
end