LISP 简单的数据库 3.7 更新记录

增加update函数以更新记录

;使用全局变量记录数据
(defvar *db* nil)

;数据记录格式
(defun make-cd (title artist rating ripped)
  (list :title title :artist artist :rating rating :ripped ripped)
)

;添加记录
(defun add-record (cd)
 ( push cd *db*)
)

;查看数据库内容
(defun dump-db()
  (dolist (cd *db*)
    (format t "~{~a: ~10t~a~%~}~%" cd))
)

;提示用户输入CD信息
(defun prompt-read (prompt)
  (format *query-io* "~a: " prompt)
  (force-output *query-io*)
  (read-line *query-io*)
)

;依次提示用户输入信息
(defun prompt-for-cd()
  (make-cd
   (prompt-read "Title")
   (prompt-read "Artist")
   ;(prompt-read "Rating")
   ;(prompt-read "Ripped [y/n]")

   ;快餐式验证数据有效性
   (or (parse-integer (prompt-read "Rating") :junk-allowed t) 0)
   (y-or-n-p "Ripped [y/n]: ")

  )
)

;批量添加数据，使用回车退出
(defun add-cds()
  (loop (add-record (prompt-for-cd))
     (if (not (y-or-n-p "Another? [y/n]:"))
	 (return)
      )
   )
)

;保存数据
(defun save-db (filename)
  (with-open-file(out filename :direction :output :if-exists :supersede)
    (with-standard-io-syntax(print *db* out))
   )
)

;载入数据
(defun load-db(filename)
  (with-open-file(in filename)
    (with-standard-io-syntax(setf *db* (read in)))
   )
)

;通过艺术家查找记录
(defun select-by-artist(artist)
  (remove-if-not #'(lambda (cd) (equal (getf cd :artist) artist)) *db*)
)

;优化查询 
(defun select(selector-fn)
  (remove-if-not selector-fn *db*)
)

;where条件判断
(defun where (&key title artist rating (ripped nil ripped-p))
  #'( lambda (cd)
      (and
        (if title (equal (getf cd :title) title) t)
	(if artist (equal (getf cd :artist) artist) t)
	(if rating (equal (getf cd :rating) rating) t)
	(if ripped-p (equal (getf cd :ripped) ripped) t)
       )
     )
)

;更新记录
(defun update(selector-fn &key title artist rating (ripped nil ripped-p))
  (setf *db*
	(mapcar #'(lambda (row) (when (funcall selector-fn row)
				  (if title (setf (getf row :title) title))
				  (if artist (setf (getf row :artist) artist))
				  (if rating (setf (getf row :rating) rating))
				  (if ripped-p (setf (getf row :ripped) ripped))
				  ) row) *db*)
   )
)

当前*DB*数据

(
(:TITLE "Title3" :ARTIST "fengda" :RATING 11 :RIPPED NIL) 
(:TITLE "Title2" :ARTIST "Artist2" :RATING 7 :RIPPED T) 
(:TITLE "Title1" :ARTIST "Artist1" :RATING 6 :RIPPED T) 
(:TITLE "Kly" :ARTIST "Gy" :RATING 9 :RIPPED T) 
(:TITLE "Lily" :ARTIST "Pgy" :RATING 8 :RIPPED T) 
(:TITLE "Roses" :ARTIST "Kathy" :RATING 7 :RIPPED T))

执行函数：

CL-USER> (update (where :artist "fengda") :artist "hahaha" :rating 22)
((:TITLE "Title3" :ARTIST "hahaha" :RATING 22 :RIPPED NIL) (:TITLE "Title2" :ARTIST "Artist2" :RATING 7 :RIPPED T) (:TITLE "Title1" :ARTIST "Artist1" :RATING 6 :RIPPED T) (:TITLE "Kly" :ARTIST "Gy" :RATING 9 :RIPPED T) (:TITLE "Lily" :ARTIST "Pgy" :RATING 8 :RIPPED T) (:TITLE "Roses" :ARTIST "Kathy" :RATING 7 :RIPPED T))

文章来源: blog.csdn.net，作者：fengda2870，版权归原作者所有，如需转载，请联系作者。

原文链接：blog.csdn.net/fengda2870/article/details/9081129