(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
$dsn
,$username
= null
,$password
= null
,$options
= null
Creates a PDO instance to represent a connection to the requested database.
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:
dsn
contains the full DSN.
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
dsn
consists of a name
name
that maps to
pdo.dsn.
in php.ini
defining the DSN string.
name
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.
PDO::__construct() throws a PDOException if the attempt
to connect to the requested database fails, regardless of which PDO::ATTR_ERRMODE
is currently set.
Example #1 Create a PDO instance via driver invocation
<?php
/* Connect to a MySQL database using driver invocation */
$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
/* Connect to an ODBC database using driver invocation */
$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
/* Connect to an ODBC database using an alias */
$dsn = 'mydb';
$user = '';
$password = '';
$dbh = new PDO($dsn, $user, $password);
?>