[{"collection":"employees","count":100,"content":{"_id":{"type":"autoincrement","autoType":"int"},"first_name":{"type":"faker","method":"FirstName"},"last_name":{"type":"faker","method":"LastName"}}}]

db.employees.update({"first_name":{"$exists":true},"last_name":{"$exists":true},"name":{"$exists":false}},[{"$set":{"name":{"$concat":["$first_name"," ","$last_name"]}}}],{"multi":true})