swift - Combine two fields into one during core data migration -

i have 2 versions of core data model different entities

i've built mappingmodel translate old model new model works 1 1 mappings

i'd combine (concatenate) 2 fields old model single field in new model. eg similar to:

newmodel.user.name = oldmodel.user.firstname + " " + oldmodel.user.lastname 

how should go this?