在Common Lisp中访问嵌套的JSON字段
我一直在尝试使用spotify API，以便熟悉常见的Lisp。这种语言与我习惯的语言有很大的不同，我担心我可能对如何解析对象和列表缺少一些理解。
当我轮询spotify API按标题查找歌曲时。它返回了很多我使用cl-json解码方法访问的json。但是，为了访问任何字段，我发现自己在进行长嵌套的car cdr组合。cl-json返回的不是listp或lista，而是一个巨大的嵌套cons列表。解析起来就像一场噩梦。我附上下面的代码作为一个例子。所以我想问的是，我错过了什么？这段代码看起来就像用LISP完成的那样笨拙和凌乱，我认为有一种很好的方法可以将所有的JSON映射到某种类型的对象或层次结构树？这将使查询变得更容易。
(ql:quickload '(:cl-json :drakma))
(defvar *auth-token*)
(defvar *results*)
(setq *url* "https://api.spotify.com/v1/search")
(push (cons "application" "json") drakma:*text-content-types*)
(setf drakma:*header-stream* *standard-output*)
(defun search-spotify (&optional (search-param "blue moon") (search-type "track") (limit 5))
"Perform a search on the API for track, artist, or album information"
(defvar complete-url "")
(defvar url nil)
(defvar params nil)
(setq url "https://api.spotify.com/v1/search")
(setq params (format nil "?q=~a&type=~a&limit=~a" (replace-all search-param " " "+") (replace-all search-type " " "+") limit))
(setq complete-url (format nil "~a~a" url params))
(print complete-url)
(setq *results* (cl-json:decode-json-from-string
(drakma:http-request complete-url
:method :get
:additional-headers `(("Authorization" . ,(format nil "Bearer ~a" (cdar *auth-token*))))
))))
(defun print-spotify-artist ()
(loop for result in (cdr (caddar *results*))
do (format t "Artist Name: ~a Spotify ID: ~a ~%" (cdadr (cddadr (caddar result))) (cdar (cdaadr (caddar result))))))运行上述代码并调用print-spotify-artist函数将打印一个列表，如下所示：
艺人名称: Eve 6 Spotify ID：https://open.spotify.com/artist/4Eqd24yS5YcxI8b6Xfuwr8艺人名称: Bill Murray Spotify ID：https://open.spotify.com/artist/3wkZ8WTrs7WcfE13voUCK1艺人名称：https://open.spotify.com/artist/0LyfQWJT6nXafLPZqxe9Of艺人名称: Pat Martino Spotify ID：https://open.spotify.com/artist/4DlMMgnldzX6OkCskmeGKz艺人名称: Jess & Zeb Spotify ID：https://open.spotify.com/artist/1oAndP8vmGtTlB6mbpieJs
示例JSON返回，对于这个示例数据，我将最大结果设置为1。请注意，它是严重嵌套的。下面是从cl-json的decode json函数返回的内容。
((:TRACKS
(:HREF
. "https://api.spotify.com/v1/search?query=open%2Broad%2Bsong&type=track&offset=0&limit=1")
(:ITEMS
((:ALBUM (:ALBUM--TYPE . "album")
(:ARTISTS
((:EXTERNAL--URLS
(:SPOTIFY . "https://open.spotify.com/artist/4Eqd24yS5YcxI8b6Xfuwr8"))
(:HREF . "https://api.spotify.com/v1/artists/4Eqd24yS5YcxI8b6Xfuwr8")
(:ID . "4Eqd24yS5YcxI8b6Xfuwr8") (:NAME . "Eve 6") (:TYPE . "artist")
(:URI . "spotify:artist:4Eqd24yS5YcxI8b6Xfuwr8")))
(:AVAILABLE--MARKETS "AD" "AR" "AT" "AU" "BE" "BG" "BO" "BR" "CA" "CH"
"CL" "CO" "CR" "CY" "CZ" "DE" "DK" "DO" "EC" "EE" "ES" "FI" "FR" "GB"
"GR" "GT" "HK" "HN" "HU" "ID" "IE" "IL" "IS" "IT" "JP" "LI" "LT" "LU"
"LV" "MC" "MT" "MY" "NI" "NL" "NO" "NZ" "PA" "PE" "PH" "PL" "PT" "PY"
"RO" "SE" "SG" "SK" "SV" "TH" "TR" "TW" "US" "UY" "VN" "ZA")
(:EXTERNAL--URLS
(:SPOTIFY . "https://open.spotify.com/album/1qJOmC60ez9RNWPg4ELMBW"))
(:HREF . "https://api.spotify.com/v1/albums/1qJOmC60ez9RNWPg4ELMBW")
(:ID . "1qJOmC60ez9RNWPg4ELMBW")
(:IMAGES
((:HEIGHT . 639)
(:URL
. "https://i.scdn.co/image/3f7891ffa993954dd72ed50245280b15f5db5844")
(:WIDTH . 621))
((:HEIGHT . 300)
(:URL
. "https://i.scdn.co/image/16f1a6277b827fd97cb450c5dc246d29c2ed1d52")
(:WIDTH . 291))
((:HEIGHT . 64)
(:URL
. "https://i.scdn.co/image/935aca4d861213415fc64f780b0e9e5a0e8d865c")
(:WIDTH . 62)))
(:NAME . "Eve 6") (:RELEASE--DATE . "1998")
(:RELEASE--DATE--PRECISION . "year") (:TYPE . "album")
(:URI . "spotify:album:1qJOmC60ez9RNWPg4ELMBW"))
(:ARTISTS
((:EXTERNAL--URLS
(:SPOTIFY . "https://open.spotify.com/artist/4Eqd24yS5YcxI8b6Xfuwr8"))
(:HREF . "https://api.spotify.com/v1/artists/4Eqd24yS5YcxI8b6Xfuwr8")
(:ID . "4Eqd24yS5YcxI8b6Xfuwr8") (:NAME . "Eve 6") (:TYPE . "artist")
(:URI . "spotify:artist:4Eqd24yS5YcxI8b6Xfuwr8")))
(:AVAILABLE--MARKETS "AD" "AR" "AT" "AU" "BE" "BG" "BO" "BR" "CA" "CH" "CL"
"CO" "CR" "CY" "CZ" "DE" "DK" "DO" "EC" "EE" "ES" "FI" "FR" "GB" "GR" "GT"
"HK" "HN" "HU" "ID" "IE" "IL" "IS" "IT" "JP" "LI" "LT" "LU" "LV" "MC" "MT"
"MY" "NI" "NL" "NO" "NZ" "PA" "PE" "PH" "PL" "PT" "PY" "RO" "SE" "SG" "SK"
"SV" "TH" "TR" "TW" "US" "UY" "VN" "ZA")
(:DISC--NUMBER . 1) (:DURATION--MS . 194866) (:EXPLICIT)
(:EXTERNAL--IDS (:ISRC . "USRC19806851"))
(:EXTERNAL--URLS
(:SPOTIFY . "https://open.spotify.com/track/7kAKO1EYHt2MVlombUuoLN"))
(:HREF . "https://api.spotify.com/v1/tracks/7kAKO1EYHt2MVlombUuoLN")
(:ID . "7kAKO1EYHt2MVlombUuoLN") (:IS--LOCAL) (:NAME . "Open Road Song")
(:POPULARITY . 44)
(:PREVIEW--URL
. "https://p.scdn.co/mp3-preview/b793285aeeb4a1176b93dc739ffb361c6aabf4e5?cid=b067abcbc67f4ceba0d61e414926c9f5")
(:TRACK--NUMBER . 5) (:TYPE . "track")
(:URI . "spotify:track:7kAKO1EYHt2MVlombUuoLN")))
(:LIMIT . 1)
(:NEXT
. "https://api.spotify.com/v1/search?query=open%2Broad%2Bsong&type=track&offset=1&limit=1")
(:OFFSET . 0) (:PREVIOUS) (:TOTAL . 43))) 回答 1
Stack Overflow用户
发布于 2018-05-31 21:06:00
Access library可能会有所帮助，它允许访问嵌套的数据结构。
(defparameter my-plist (list :foo "foo" :bar "bar"))
;; bar is a plist
(defclass obj-test ()
((foo :accessor foo :initarg :foo :initform :foo)
(bar :accessor bar :initarg :bar :initform (copy-list MY-PLIST))))
(defvar my-obj ((make-instance 'obj-test))
(accesses MY-OBJ 'bar 'foo) ;; => "foo"有一种方法可以使用虚线路径，如果你喜欢的话。
Access是经过实战测试的，它是Djula模板引擎的核心，是Quicklisp上下载量最大的库之一。
Access还允许跨数据结构进行一致的访问。
更深层次的概述：https://lisp-journey.gitlab.io/blog/generice-consistent-access-of-data-structures-dotted-path/
https://stackoverflow.com/questions/50621703
复制相似问题