[{_id:ObjectId("64197b3c022b94220a7954e9"),name:"Frank",gender:"male",_class:"com.holdsport.model.person"},{_id:ObjectId("64197bd6018930affa3ff88f"),name:"Anna",gender:"female",_class:"com.holdsport.model.person"},{_id:ObjectId("64197be3a5c866cb5a93bf3e"),name:"Mary",gender:"female",_class:"com.holdsport.model.person"}]

db.collection.update({gender:{$in:["male","female"]}},[{$set:{_class:{$cond:[{$eq:["$gender","male"]},"com.holdsport.model.male","com.holdsport.model.female"]}}}],{multi:true})