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
string
$dsn,?string
$username = null,?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
dsnparameter supports three different methods of specifying the arguments required to create a database connection:- Driver invocation
-
dsncontains the full DSN. - URI invocation
-
dsnconsists ofuri: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
-
dsnconsists of a namenamethat maps topdo.dsn.in php.ini defining the DSN string.nameNote:
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.
- passwd
-
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
/* 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);
?>
