Costruire e mantenere un database in Emacs?

Question

Stavo leggendo la sezione Simple Database del libro di Peter Siebel Practical Common Lisp con l'idea di mantenere un piccolo database di circa 50.000 record. Ho pensato che farlo in Emacs potesse essere un esercizio interessante e utile. Emacs Lisp è in qualche modo compatibile con CL tranne alcuni notable differences. La funzione nella funzione utilizzata nell'esempio precedente rappresenta una differenza importante.

Ecco il codice che contiene tutto il necessario per costruire, salvare e caricare il database in CL. Può essere modificato per funzionare bene in Emacs? Ho omesso lo selezionare e dove le funzioni ma vorrei includerle. Forse c'è un modo migliore di costruire e mantenere un database di Emacs? Personalmente, sto usando questo come esercizio per imparare CL e risolvere un problema esistente.

 
;; Simple Common Lisp database 
;; http://www.gigamonkeys.com/book/practical-a-simple-database.html 
;; 
(defvar *db* nil) 

(defun make-cd (title artist rating ripped) 
    (list :title title :artist artist :rating rating :ripped ripped)) 

(defun add-record (cd) (push cd *db*)) 

(defun dump-db() 
    (dolist (cd *db*) 
    (format t "~{~a:~10t~a~%~}~%" cd))) 

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

(defun load-db (filename) 
    (with-open-file (in filename) 
    (with-standard-io-syntax 
     (setf *db* (read in))))) 
; === 
; 
; Add some records 
; 
(add-record (make-cd "Roses" "Kathy Mattea" 7 t)) 
(add-record (make-cd "Fly" "Dixie Chicks" 8 t)) 
(add-record (make-cd "Home" "Dixie Chicks" 9 t)) 

; (dump-db) 
; (save-db "cd.db") 
; (load-db "cd.db") 

Answer 1

Quando ho cercato di scrivere una libreria di ebook per Emacs, ho memorizzato il record in un elenco, salvarlo su disco di tanto in tanto. Quando la lunghezza dell'elenco ha superato circa cinquemila record, la performance ha subito.

Ecco alcune funzioni dal codice:

(defun bread-library-load-db() 
"Loads the list of books from disk file to the variable bread-library-db" 
     (if (file-exists-p bread-library-file) 
      (with-temp-buffer 
     (insert-file-contents bread-library-file) 
     (setq bread-library-db (read (current-buffer)))) 
     (setq bread-library-db '()))) 

(defun bread-library-add-book (file) 
    "Attempts to get metadata from file, then prompts for 
confirmation (or modification) of these metadata, then adds the 
book to the database and saves it. Intended use: from dired." 
    (if (assoc file bread-library-db) 
     (error "File is already in the database") 
    (progn 
     (let ((metadata (bread-get-metadata file))) 
    (let ((filename (nth 0 metadata)) 
      (author (read-from-minibuffer 
       "Author: " 
       (nth 1 metadata))) 
      (title (read-from-minibuffer 
       "Title: " 
       (nth 2 metadata))) 
      (genre (read-from-minibuffer "Genre: " (nth 3 metadata))) 
      (tags (read-from-minibuffer "Tags (separated and surrounded by colons): " ":")) 
      (desc (nth 4 metadata))) 
     (setq bread-library-db (cons 
        (list filename author title tags "TOREAD" genre nil desc) 
        bread-library-db)))) 
     (bread-library-save-db bread-library-db)))) 

(defun bread-library-save-db (db) 
    "Save the library database to a file." 
    (message "Saving Bread library database...") 
    (with-temp-buffer 
     (insert "; 1.path 2.author 3.title 4.tags 5.state 6.genre 7.priority 8.description") 
     (print db (current-buffer)) 
     (write-file bread-library-file)) 
    (message "Saving Bread library database...done")) 

Answer 2

Ecco la mia soluzione:

 

(defvar *db* nil) 

(setq *db*()) 

(defun make-cd (title artist rating ripped) 
    (list :title title :artist artist :rating rating :ripped ripped)) 

(defun add-record (cd) (push cd *db*)) 

(defun init() 
    (progn 
    (add-record (make-cd "Roses" "Kathy Mattea" 7 t)) 
    (add-record (make-cd "Fly" "Dixie Chicks" 8 t)) 
    (add-record (make-cd "Home" "Dixie Chicks" 9 t)) 
    )) 

(defun save-db (filename) 
    (with-temp-buffer 
    (print *db* (current-buffer)) 
    (write-file filename)) 
    (message "Saving database...done") 
) 

(defun load-db (filename) 
    (with-temp-buffer 
    (insert-file-contents filename) 
     (setq *db* (read (current-buffer))))) 

(defun dump-db() 
    (dolist (cd *db*) 
    (print cd))) 


;; Test in M-x lisp-interaction-mode 
;;(init) 
;;(save-db "cd.db") 
;*db* 
;(add-record (make-cd "Born To Run" "Bruce Springsteen" 10 t)) 
;(add-record (make-cd "The River" "Bruce Springsteen" 10 t)) 
;(add-record (make-cd "Nebraska" "Bruce Springsteen" 10 t)) 
;(add-record (make-cd "Human Touch" "Bruce Springsteen" 10 nil)) 
;;(save-db "cd.db") 
;(setq *db*()) 
;;(load-db "cd.db") 
;*db*