自动生成ID期间clojure URL缩短器中的错误

我在Clojure编程中遇到了一段代码，它有缺陷。我是Clojure的新手，不知道代码中的bug在哪里

(ns ring-tutorial.core
  (:require [compojure.handler :as ch]
        [compojure.core :refer [GET PUT POST defroutes]]
        [compojure.route :as cr]
        [ring.util.response :as response]))

(def ^:private counter (atom 0))
(def ^:private mappings (ref {}))

(defn url-for
[id]
(@mappings id))

(defn shorten!
 "Stores the given URL under a new unique identifier and returns it as a string."
 ([url]
 (let [id (swap! counter inc)
       id (Long/toString id 36)] ;;convert to base 36 string
   (or (shorten! url id)
       (recur url))))
([url id] ;;url is provided with an id.
 (dosync
  (when-not (@mappings id)
    (alter mappings assoc id url)
    id))))

(defn retain
 [& [url id :as args]]
(if-let [id (apply shorten! args)]
{:status 201
  :headers {"Location" id}
 :body (list "URL " url " assigned the short identifier " id " \n")}
{:status 409 :body (format "Short URL %s is already taken \n " id)}))

(defn redirect
 [id]
(if-let [url (url-for id)]
(ring.util.response/redirect url) ;;Appropriately redirect the URL based on ethe ID.
{:status 404 :body (str "No such short URL: \n" id)})) ;;Return a 404 if no URL for the particular ID found.

(defroutes app*
 (GET "/" request "Hello World!")
 (PUT "/:id" [id url] (retain url id))
 (POST "/" [url ] (retain url))
 (GET "/:id" [id] (redirect id))
 (GET "/list/" [] (interpose "\n" (keys @mappings)))
 (cr/not-found "Its a 404!\n"))

(def app (ch/api #'app*))

当我运行$CURL-X POST'localhost:8080/？url=' 我得到的URL已被赋予标识符1 当我重新运行命令时，我得到的URL已被赋予标识符2，但它应该标记一个错误，表明yahoo.com已经具有标识符1

这是一个错误，我可以看到，它在缩短！功能，但无法更正它

---

谢谢

您的

映射

ref指向一个从短ID到长URL的映射。在

中缩短函数，您需要获取一个URL，并查看是否已经为其分配了一个ID。相反，您每次都会生成一个新ID，并在地图中查找它，以查看是否为其分配了URL，这永远不会发生

要解决这个问题，您需要维护长URL到短ID的第二个映射。在
dosync
块中，您将首先在这个新映射中查找URL，如果找不到URL，则生成一个ID并将URL、ID对添加到两个映射中。
因此，我应该创建一个名为mappings2{}的新引用。然后（@mappings2 url）。当不在dosync内时，还有另一个吗？比如（dosync（当不是（@mappings2 url）什么的时候？）我有点困惑，一些代码真的会有帮助