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PDO::__construct

(PHP 5 >= 5.1.0, 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 [, string $password [, array $options ]]] )

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.

Return Values

Returns a PDO object on success.

Errors/Exceptions

PDO::__construct() throws a PDOException if the attempt to connect to the requested database fails.

Examples

Example #1 Create a PDO instance via driver invocation


<?php
/* Connect to an ODBC database using driver invocation */
$dsn = 'mysql:dbname=testdb;host=127.0.0.1';
$user = 'dbuser';
$password = 'dbpass';

try {
    $dbh = new PDO($dsn, $user, $password);
} catch (PDOException $e) {
    echo 'Connection failed: ' . $e->getMessage();
}

?>

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 = '';

try {
    $dbh = new PDO($dsn, $user, $password);
} catch (PDOException $e) {
    echo 'Connection failed: ' . $e->getMessage();
}

?>

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 = '';

try {
    $dbh = new PDO($dsn, $user, $password);
} catch (PDOException $e) {
    echo 'Connection failed: ' . $e->getMessage();
}

?>

Note:
Before PHP5.3, a class which extends PDO and implements __call magic will always receive lower case $method.

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User Contributed Notes 7 notes

down

Kiipa at live dot com ¶

1 year ago


To get UTF-8 charset you can specify that in the DSN.

$link = new PDO("mysql:host=localhost;dbname=DB;charset=UTF8");

down

Anonymous ¶

6 months ago


To connect to the database via a function use this and call the getConnection function in the class constructor.

<?php
class Connection{

    protected $db;

    public function Connection(){

    $conn = NULL;

        try{
            $conn = new PDO("mysql:host=localhost;dbname=dbname", "dbuser", "dbpass");
            $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
            } catch(PDOException $e){
                echo 'ERROR: ' . $e->getMessage();
                }    
            $this->db = $conn;
    }
    
    public function getConnection(){
        return $this->db;
    }
}

?>

down

piotrekkr at o2 dot pl ¶

4 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.

down

Victor T. ¶

4 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\''));

?>

down

subme at interia dot pl ¶

5 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';
?>

down

Anonymous ¶

1 year 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.

down

-72

Mitsuaki Ishimoto ¶

4 years ago


You have to use the following option "MYSQL_ATTR_READ_DEFAULT_FILE" to prevent someone from attacking your system by SQL Injection.

<?php
$dsn = 'mysql:host=' . DB_HOST . ';dbname=' . DB_NAME;
$dbh = new PDO(
    $dsn,
    DB_USER,
    DB_PASS,
    array(
        PDO::MYSQL_ATTR_READ_DEFAULT_FILE => '/etc/my.cnf'
    )
);
$dbh->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
?>

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