Spring data MongoDb cannot convert proxy bean - spring

Question

I'm using Spring AOP with AspectJ and Spring Data MongoDb and am having a world of trouble persisting objects.
In this case, I have an AclEntryDaoImpl that exposes AclEntryImpl. When AclEntryImpl is provided a Principal that is a standard Java object (a "non-Spring" bean), mongoTemplate.save() works as expected. However when Principal is a Spring bean, Mongo is unable to convert the object and results in a MappingException org.springframework.data.mapping.model.MappingException: No id property found on class class com.sun.proxy.$Proxy33. All my objects need to be Spring beans so that (a) I keep my objects decoupled and (b) my AOP (LoggingAspect) is invoked.
Lastly, I cannot take advantage of Spring converters because Mongo sees the target object AclEntryImpl as a proxy com.sun.proxy.$Proxy33 and so Converter<Principal, DBObject> is never invoked.
Any and all help would be greatly appreciated!
Snippets:
Here's my Spring XML configuration:
<beans>
<context:component-scan base-package="a.b" />
<context:property-placeholder location="config.properties" />
<aop:aspectj-autoproxy />
<bean id="loggingAspect" class="a.b.LoggingAspect" />
<mongo:db-factory host="${database.host}" port="${database.port}" dbname="${database.dbname}" />
<bean id="mongoTemplate" class="org.springframework.data.mongodb.core.MongoTemplate">
<constructor-arg name="mongoDbFactory" ref="mongoDbFactory" />
</bean>
<bean id="aclEntryDao" class="a.b.AclEntryDaoImpl">
<lookup-method name="createAclEntry" bean="aclEntry" />
</bean>
</beans>
AclEntryImpl:
#Document
#Component
#Scope("prototype")
public class AclEntryImpl implements AclEntry {
#Id
private String id;
private String service;
#DBRef #Expose
private Principal principal;
#Expose
private boolean accessGranted;
#Expose
private List<Permission> permissions;
#Override #Loggable #MongoSaveReturned
public AclEntry save() {
return this;
}
...getters and setters...
}
AclEntryDaoImpl:
#Repository
public abstract class AclEntryDaoImpl implements AclEntryDao {
#Override #Loggable
public AclEntry addEntry(String serviceName, Principal principal, Permission[] permissions, boolean accessGranted) throws Exception {
AclEntry entry = createAclEntry(); //<-- Spring lookup-method
entry.setService(serviceName);
entry.setPrincipal(principal); //<-- com.sun.proxy.$Proxy33
entry.setAccessGranted(accessGranted);
for (Permission permission : permissions) {
if (!entry.addPermission(permission)) {
return null;
}
}
return entry.save();
}
... other DAO methods ...
}
LoggingAspect:
#Aspect
public class LoggingAspect {
#Autowired
private MongoTemplate mongoTemplate;
#Pointcut("execution(!void a.b..*.*(..))")
public void returningMethods() {}
#AfterReturning(pointcut="returningMethods() && #annotation(MongoSaveReturned)", returning="retVal")
public Object mongoSaveReturnedAdvice(Object retVal) {
Logger logger = null;
try {
logger = getLogger(retVal);
mongoTemplate.save(retVal); //<-- throws MappingException
log(logger, "save: " + retVal.toString());
} catch (Exception e) {
log(logger, "throw: " + e.toString());
}
return retVal;
}
... other logging methods ...
}