在Datascript中，如何从另一个属性的值创建新属性？

(ns my-namespace
  (:require [datascript.core :as d]))

(def conn (d/create-conn {:schema {:person {:name {:db/valueType :db.type/string}
                                              :age {:db/valueType :db.type/long}}}}))

(defn create-new-property [db person-id]
  (let [new-property-value (d/q '[:find ?age
                                  :in $ ?person
                                  :where [?person :person/age ?age]]
                                db person-id)]
    (d/transact! conn [[:db/add person-id :person/new-property [:db/attr-id :person/age] new-property-value]
                       [:db/txInstant (java.util.Date.)]])))

;; 调用示例
(create-new-property conn 1)