Amber is independent of your choice of model architectures. We (Core members) have built the ORM Granite. We also think Jennifer built by Roman Kalnytskyi is a good option.
Granite provides a light weight ORM that is focused on taking the results of your query and mapping them to your model. It does not try to shield you from the SQL that lies underneath the mapping. It provides a couple conveniences like
destroy for simple INSERT, UPDATE and DELETE statements. It provides
all to query the database. It also has basic one-to-many relationships with
Jennifer provides an more full featured ORM with a full featured DSL for queries and follows the ActiveRecord pattern found in Rails. If you are looking for a full featured ORM, Jennifer may be your choice of ORM.