CakeFest 2024: The Official CakePHP Conference

PDO::__construct

(PHP 5 >= 5.1.0, PHP 7, PHP 8, PECL pdo >= 0.1.0)

PDO::__construct Crée une instance PDO qui représente une connexion à la base

Description

public PDO::__construct(
    string $dsn,
    ?string $username = null,
    ?string $password = null,
    ?array $options = null
)

Crée un objet PDO qui représente une connexion à la base.

Liste de paramètres

dsn

Le Data Source Name, ou DSN, qui contient les informations requises pour se connecter à la base.

En général, un DSN est constitué du nom du pilote PDO, suivi d'une syntaxe spécifique au pilote. Plus de détails sont disponibles dans la documentation PDO de chaque pilote.

Le paramètre dsn supporte trois méthodes différentes pour spécifier les arguments nécessaires à la création de la base de données :

Appel pilote

dsn contient le DSN complet.

Appel URI

dsn est constitué de uri: suivi par une URI qui définit la localisation du fichier contenant la chaîne de DSN. L'URI peut spécifier un fichier local ou distant.

uri:file:///path/to/dsnfile

Aliasing

dsn est constitué d'un nom name qui correspond à pdo.dsn.name dans le fichier php.ini, et qui définit la chaîne DSN.

Note:

L'alias doit être défini dans le fichier php.ini, et non pas dans un fichier .htaccess ou httpd.conf

username

Le nom d'utilisateur pour la chaîne DSN. Ce paramètre est optionnel pour certains pilote PDO.

password

Le mot de passe de la chaîne DSN. Ce paramètre est optionnel pour certains pilote PDO.

options

Un tableau clé=>valeur avec les options spécifiques de connexion.

Erreurs / Exceptions

PDO::__construct() émet une exception PDOException si la tentative de connexion à la base de données échoue, peu importe le PDO::ATTR_ERRMODE actuellement définit.

Exemples

Exemple #1 Crée une instance PDO via une invocation de pilote

<?php

$dsn
= 'mysql:dbname=testdb;host=127.0.0.1';
$user = 'dbuser';
$password = 'dbpass';

$dbh = new PDO($dsn, $user, $password);

?>

Exemple #2 Crée une instance PDO via une invocation URI

L'exemple ci-dessous suppose que le fichier /usr/local/dbconnect existe avec des droits d'accès qui permettent à PHP d'y accéder. Le fichier contient alors le DSN de PDO, pour se connecter à une base de données DB2, avec le pilote PDO_ODBC :

odbc:DSN=SAMPLE;UID=john;PWD=mypass

Le script PHP peut alors créer une connexion de base de données, en passant dans l'URL le paramètre uri: et en pointant sur l'URI du fichier :

<?php

$dsn
= 'uri:file:///usr/local/dbconnect';
$user = '';
$password = '';

$dbh = new PDO($dsn, $user, $password);

?>

Exemple #3 Crée une instance PDO avec un alias

L'exemple ci-dessous suppose que le fichier php.ini contient la directive suivant pour activer une connexion à un serveur MySQL, avec l'alias mydb:

[PDO]
pdo.dsn.mydb="mysql:dbname=testdb;host=localhost"
<?php

$dsn
= 'mydb';
$user = '';
$password = '';

$dbh = new PDO($dsn, $user, $password);

?>

add a note

User Contributed Notes 16 notes

up
123
Kiipa at live dot com
10 years ago
To get UTF-8 charset you can specify that in the DSN.

$link = new PDO("mysql:host=localhost;dbname=DB;charset=UTF8");
up
5
theking2 at king dot ma
1 year ago
A generic pattern to connect to a mariadb or mysql database using a settings file

<?php
$_SETTINGS
= parse_ini_file('./settings.ini', true);

$db = new \PDO(
"mysql:hostname={$_SETTINGS['db']['host']};dbname={$_SETTINGS['db']['name']}",
$_SETTINGS['db']['user'],
$_SETTINGS['db']['pass'],
[
\PDO::ATTR_DEFAULT_FETCH_MODE => \PDO::FETCH_ASSOC,
\PDO::MYSQL_ATTR_INIT_COMMAND => "SET NAMES 'utf8mb4'"
]
);
?>
You might not need the options depicted here but I find them convenient.

Works with a settings.ini file containing for instance:
[db]
host = "localhost"
name = "dbname"
user = "dbuser"
pass = "dbpassword"
up
41
subme at interia dot pl
15 years ago
To specify a database connection port use the following DSN string

<?php
$dsn
= 'mysql:dbname=testdb;host=127.0.0.1;port=3333';
?>
up
8
Aymeric S
3 years ago
When trying to connect to a local database, it seems "uri:file:///" is no longer needed. Just write the PDO pilot name followed by the absolute path of the file.
Example : sqlite:C:\VirtualHosts\phpliteadmin\dbs\surveillance_logeas.s3DB
up
28
piotrekkr at o2 dot pl
13 years ago
To connect throught unix socket you need to use
<?php
$dsn
= 'mysql:dbname=testdb;unix_socket=/path/to/socket';
?>

You musn't specify host when using socket.
up
21
daviddlavier at gmail dot com
8 years ago
I'd like to point out that in PHP 7.0 in the dsn parameter you can't use 'host=localhost' to solve this you can use 'host=127.0.0.1' instead.
up
2
Michal Stefanak
1 year ago
If you override PDO with own class and you want to implement alias from php.ini, you have to get it with `get_cfg_var` instead of `ini_get`.

<?php
class PDO extends \PDO
{
public function
__construct(string $dsn, ?string $username = null, ?string $password = null, ?array $options = null)
{
//alias
if (!str_contains($dsn, ':')) {
$dsn = get_cfg_var('pdo.dsn.' . $dsn);
if (!
$dsn) {
throw new
PDOException('Argument #1 ($dsn) must be a valid data source name');
}
}

// your additional logic

parent::__construct($dsn, $username, $password, $options);
}
}
?>
up
8
Francesco Montanari
3 years ago
Most of the information in the comment here is outdated or wrong.

You do can use host=localhost to connect via socket, which is faster than TCP, so setting 127.0.0.1 is a performance loss.

To use proper utf you should use utf8mb4, for example:

$db = new PDO('mysql:host=' . DATABASE_HOST . ';dbname='. DATABASE_NAME .';charset=utf8mb4', DATABASE_USER, DATABASE_PASSWORD);
up
14
Victor T.
14 years ago
If you use the UTF-8 encoding, you have to use the fourth parameter :

<?php
$db
= new PDO('mysql:host=myhost;dbname=mydb', 'login', 'password', array(PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES \'UTF8\''));
?>
up
0
max1josef
10 months ago
SQLite3: by default, the database file is created on opening if it does not exist (PDO::SQLITE_OPEN_CREATE).

<?php
$dsn
= 'sqlite:D:\Databases\non_existing.db'; // file does not exist

try {
$dbh = new PDO($dsn);
}
catch(
PDOException $e) {
print
$e->getMessage();
}
?>

No Exception is thrown, instead file "non_existing.db" will be created. To avoid this, use:

<?php
$dsn
= 'sqlite:D:\Databases\non_existing.db';
$options = [
PDO::SQLITE_ATTR_OPEN_FLAGS => PDO::SQLITE_OPEN_READWRITE,
];

try {
$dbh = new PDO('sqlite:D:\Databases\non_existing.db', null, null, $options);
}
catch(
PDOException $e) {
print
$e->getMessage();
}
?>
This will ouput:
SQLSTATE[HY000] [14] unable to open database file

If you want to open the database read-only, use PDO::SQLITE_OPEN_READONLY.
up
0
453034559 at qq dot com
2 years ago
// set DEFAULT_FETCH_MODE
<?php
try {
$p = new PDO("mysql:host=$db_host;port=$db_port;dbname=$db_dbname", $db_user, $db_pass,array(
PDO::ATTR_DEFAULT_FETCH_MODE =>PDO::FETCH_ASSOC,
PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES utf8', //after php5.3.6
));
//$p->exec('SET NAMES utf8');
} catch (PDOException $e) {
print
"Error!: " . $e->getMessage() . "<br/>";
die();
}
?>
up
0
Anonymous
10 years ago
Sqlite:

<?php
try{
$pdo = new PDO('sqlite:example.db');
}catch (
PDOException $e){
die (
'DB Error');
}
?>

If 'example.db' does not exist, no exception is thrown but the file 'example.db' is created.
up
-2
ohcc at 163 dot com
8 years ago
You will get a fatal error if you don't catch the exception threw by PDO when it fails to connect to the database server like this.

Fatal error: in xxx.php on line xx

This error neither can be handled by error handlers nor can it be erased by the @ sign, which can make your script uncontrollable.

<?php
$db
= new pdo('mysql:host=127.0.0.1;port=3306;dbname=mysql;charset=utf8','user','password',array(
PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
));
?>

You should always try ... catch ...

<?php
try{
$db = new pdo('mysql:host=127.0.0.1;port=3306;dbname=mysql;charset=utf8','user','password',array(
PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
));
}catch(
PDOException $pe){
echo
$pe->getMessage();
}
?>
up
-3
berk0081 at umn dot edu
9 years ago
Although not explicitly stated, parameters in the PDO $dsn string may be case-sensitive on some platforms or drivers.

<?php
// The dbname will not be parsed with incorrect casing:
$pdo = new PDO("mysql:host=hostname;DBName=database", "user", "password");

// The correct dbname is lowercase, as displayed in the manual:
$pdo = new PDO("mysql:host=hostname;dbname=database", "user", "password");
?>
up
-9
srycroft at excelsystems dot com
7 years ago
For IBM i / iSeries / AS400 DB2 connections, you can specify system naming and library lists for php_pdo modules > 1.3.3-sg2

<?php
$pdo
= new PDO(
'ibm:' . $host,
$user,
$password,
array(
PDO::I5_ATTR_DBC_SYS_NAMING => true,
PDO::I5_ATTR_DBC_LIBL => "QGPL QSYS"
)
);
?>

See http://yips.idevcloud.com/wiki/index.php/XMLSERVICE/PHPPDOChangeLog
up
-31
olivernybroe at gmail dot com
7 years ago
The PDO connection is case-sensitive, this means that you cannot write
`$PDO = new PDO("MySQL:DBName=dbname;host=localhost");`
You would have to write it
`$PDO = new PDO("mysql:dbname=dbname;host=localhost");`

The difference here is that `mysql` and `dbname` is with all lower-case.

Some IDE's like PHPStorm will show a `TYPO ERROR`, at `dbname` if it's written with lower-case only, this is just to be ignored and have been reported to PHPStorm for them to fix. (Currrent version 10.0.2)
To Top