Hello,
there's an example in the tests sources, you can download the sources or see it on fisheye:
PersonPKBridgePersonPKPersonRemember your primary keys must have an equals implementation, you basically need to create a new instance of the PK type and set the parts of it by parsing the string(s) from the Document in such a way that you'll be able to load the full entity from the primary key.
Note that the example is encoding the id in a single field, and also using two fields to store both
firstName and
lastName separately.