PDO::__construct

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

PDO::__construct Creates a PDO instance representing a connection to a database

Description

public PDO::__construct(
    string $dsn,
    ?string $username = null,
    #[\SensitiveParameter] ?string $password = null,
    ?array $options = null
)

Creates a PDO instance to represent a connection to the requested database.

Parameters

dsn

The Data Source Name, or DSN, contains the information required to connect to the database.

In general, a DSN consists of the PDO driver name, followed by a colon, followed by the PDO driver-specific connection syntax. Further information is available from the PDO driver-specific documentation.

The dsn parameter supports three different methods of specifying the arguments required to create a database connection:

Driver invocation

dsn contains the full DSN.

URI invocation

dsn consists of uri: followed by a URI that defines the location of a file containing the DSN string. The URI can specify a local file or a remote URL.

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

Aliasing

dsn consists of a name name that maps to pdo.dsn.name in php.ini defining the DSN string.

Note:

The alias must be defined in php.ini, and not .htaccess or httpd.conf

username

The user name for the DSN string. This parameter is optional for some PDO drivers.

password

The password for the DSN string. This parameter is optional for some PDO drivers.

options

A key=>value array of driver-specific connection options.

Errors/Exceptions

PDO::__construct() throws a PDOException if the attempt to connect to the requested database fails, regardless of which PDO::ATTR_ERRMODE is currently set.

Examples

Example #1 Create a PDO instance via driver invocation

<?php

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

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

?>

Example #2 Create a PDO instance via URI invocation

The following example assumes that the file /usr/local/dbconnect exists with file permissions that enable PHP to read the file. The file contains the PDO DSN to connect to a DB2 database through the PDO_ODBC driver:

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

The PHP script can then create a database connection by simply passing the uri: parameter and pointing to the file URI:

<?php

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

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

?>

Example #3 Create a PDO instance using an alias

The following example assumes that php.ini contains the following entry to enable a connection to a MySQL database using only the 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 14 notes

up
125
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
44
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
6
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
8
Aymeric S
4 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
29
piotrekkr at o2 dot pl
14 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
20
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
10
Francesco Montanari
4 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
1
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
13
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
1
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
11 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
-2
max1josef
1 year 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.
To Top