How to export GUID of objects?

Dear, When i create a rest api with export_mapping.  I want to return objects with GUID. Not find out where to select this field on MessageDefinition and Export mapping. What i can do now is:  use a micoflow to get object id and convert this object to a non-persistence object and return. 2nd option is : add a Redundancy property, add a after commit event handler to update this property,  Select this Redundancy property in message difinition. But,  I think mendix shoud has a simple way to do this,  is there? Thanks.  
1 answers

Assuming you use the GUID as key;

The GUID isn't accessible as normal attributes are. My advise is to never use them in integrations as they are internal app properties. 

What I would do is, add a autonumber attribute to your entity and use that as key in your integrations