<entity class="test.A">
 		<customizer class="test.customizer.TestCustomizer"/>
		<attributes>
			<id name="id">
				<generated-value strategy="IDENTITY"/>
			</id>
                        <basic ...
			<one-to-one name="B">
				<join-column name="id_b"/>
			</one-to-one>
		</attributes>
	</entity>
	<entity class="test.B">
		<table name="person"/>
		<attributes>
			<id name="id">
			</id>
			<basic ...
		</attributes>
	</entity>
</entity-mappings>

TransformationMapping mapping = new TransformationMapping();  mapping.addFieldTransformer("test.id_b", new FieldTransformer() { ...
descriptor.addMapping(mapping);

tmapping.setAttributeTransformer(new AttributeTransformer() {
			
			@Override
			public void initialize(AbstractTransformationMapping map) {
			}
			
			@Override
			public Object buildAttributeValue(Record record, Object object, Session session) {
				UnitOfWork uow = session.acquireUnitOfWork();
				B b = new B();
				b.setId(Long.valueOf((long)3));
				B bc = (B)uow.readObject(b);
				A a = (A)object;
				a.setB(bc);
				return pc;
			}
		});
		descriptor.addMapping(tmapping);