Summary

Go driver's UpdateMany doesn't update fields using existing fields in object.
 
col.UpdateMany(ctx,bson.M{“id”:123},bson.D{"$set", bson.D{“PreviousRecord”,"$CurrentRecord")}}

This command will update object:
{{

{ id:123, PreviousRecord:"old", CurrentRecord:"new" }

}}

as:
{{

{ id:123, PreviousRecord:"$CurrentRecord", CurrentRecord:"new" }

}}

MongoDB 4.4 (docker image mongo:4.4); GO-driver 1.7.1