5.6 Database operating ¶

GNU Artanis supports mysql/postgresql/sqlite3. We use mysql as an example here.

Please ensure that your DB service was started before you run this code.

If you encounter any problems, it’s very likely it’s with your DB config.

You can use a DB (such as mysql) with GUI tools such as "adminer", independently of the running web-server, e.g. artanis-based.

(use-modules (artanis artanis))
(init-server)
(define conn (connect-db 'mysql #:db-username "your_db_username"
                         #:db-name "your_db_name" #:db-passwd "your_passwd"))
(define mtable (map-table-from-DB conn))
((mtable 'create 'Persons '((name varchar 10)
                            (age integer)
                            (email varchar 20)))
 'valid?)
;; ==> #t
(mtable 'set 'Persons #:name "nala" #:age 20 #:email "nala@artanis.dev")
(mtable 'get 'Persons #:columns '(name email))
;; ==> ((("name" . "nala") ("email" . "nala@artanis.com")))

• map-table-from-DB is the GNU Artanis API handling tables in a DB. Here, we define this mapping as the var mtable.

• We can use mtable to handle tables, you can get the values from a table with the ’get command.

• mtable is a function which accepts the first argument as a command, say ’create, which is a command to create a new table. ’set is used to insert/update values in the table. And the ’get command to fetch the values of specific columns.

• The second argument of mtable is the name of the table as you can guess. Please note that it is case sensitive, while the column name isn’t.

• The ’create command returns a function too, which also accepts an argument as a command. Here, we use the ’valid? command to check if the table has been created successfully.

This was just a simple introduction. You may read the DB section in this manual for details.

Of course, you can use DB in your web application.

(get "/dbtest" #:conn #t ; apply for a DB connection from pool
     (lambda (rc)
       (let ((mtable (map-table-from-DB (:conn rc))))
         (object->string
          (mtable 'get 'Persons #:columns '(name email))))))

(run #:use-db? #t #:dbd 'mysql #:db-username "your_db_username"
     #:db-name "your_db_name" #:db-passwd "your_passwd" #:port 8080)

Now, try loading http://localhost:8080/dbtest in your browser.

Here is quick explanation:

• The keyword-value pair #:conn #t means applying for a DB connection from connection-pool. Then you can use (:conn rc) to get the allocated connection for DB operations.
• Finally, the handler needs to return a string as the HTTP response body, so in this example,

we have to use the Guile API object->string to convert the query result into a string.

Exercise: Return a beautiful table in HTML rather than using object->string.