Howto store java.lang.Class objects in db4o

I ran into an interesting problem when querying our db4o NoSQL database the other day. I had an object with a java.lang.Class as one of it's fields. Every time i queried for this object the Class field was set to null. Below is an example of what my model class looked like:

public class MessageServicePreference {
    private final UUID userId;
    private String serviceName;
    private Class<?> serviceClass;

    public MessageServicePreference(UUID userId, MessageService service) {
        this.userId = userId;
        this.serviceName = service.getName();
        this.serviceClass = service.getClass(); //gets the actual implementation class, not MessagingService.class
    }

    public UUID getUserId() {
        return userId;
    }

    public String getServiceName() {
        return serviceName;
    }

    public Class<?> getServiceClass() {
        return serviceClass;
    }

    public void setService(MessageService service) {
        serviceName = service.getName();
        serviceClass = service.getClass();
    }
}

So, like i said when i queried for this class using db4o:

public MessageServicePreference getPreferenceFor(User user) {
    MessageServicePreference preference = null;
    ObjectContainer db = DatabaseConnectionPool.aquireConnection();
    try {
        Query query = db.query();
        query.constrain(MessageServicePreference.class);
        query.descend("userId").constrain(user.getId());
        List<MessageServicePreference> preferences = query.execute();
        if (!preferences.isEmpty()) {
            preference = preferences.get(0);
        }
        return preference;
    } finally {
        DatabaseConnectionPool.releaseConnection(db);
    }
}

This query would return a MessageServicePreference, but when i called .getServiceClass() it would return null. So, by inspecting the java.lang.Class source code i found that all of the fields in the source were either static or transient, and db4o doesn't persist static or transient fields. Then it i found the method java.lang.Class.forName(String className) and came up with the following solution:

public class MessageServicePreference {
    private final UUID userId;
    private String serviceName;
    private String serviceClassName;

    public MessageServicePreference(UUID userId, MessageService service) {
        this.userId = userId;
        this.serviceName = service.getName();
        this.serviceClassName = service.getClass().getName(); //gets the actual implementation class's fully qualified name (package.to.class.MessageServiceImpl)
    }

    public UUID getUserId() {
        return userId;
    }

    public String getServiceName() {
        return serviceName;
    }

    public Class<?> getServiceClass() {
        return Class.forName(serviceClassName);
    }

    public void setService(MessageService service) {
        serviceName = service.getName();
        serviceClassName = service.getClass().getName();
    }
}

This new model class saves all of it's data properly in db4o and when queried populates the serviceClassName field correctly, which in turn makes the getServiceClass() method work as expected.