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xPDO Database Connections

Database connectivity in xPDO is done in the constructor. The xPDO object can only hold one database connection per instance, but you are free to instantiate as many xPDO instances as you need. The syntax of the constructor is such:

function xPDO($dsn, $username= '', $password= '', $options= array(), $driverOptions= null)

So let's say we want to connect to a localhost database named 'test' on port 3306, with a utf-8 charset:

$dsn = 'mysql:host=localhost;dbname=test;port=3306;charset=utf8';
$xpdo = new xPDO($dsn,'username','password');

And you're done!

Optionally verify the connection, by simply adding the following line afterward

echo $o=($xpdo->connect()) ? 'Connected' : 'Not Connected';

xPDO creates a PDO object, and thus connects to the database, only when a PDO method is called and the connection is needed. This connect-on-demand feature allows xPDO caching to work without a database connection being required (assuming everything is cached).

More information on these parameters can be found on The xPDO Constructor page.

Once you're connected, you'll need to load your package.

Example Connection

Here's an example script that can be used to connect to a foreign database:


define('MODX_CORE_PATH', '/path/to/revo/core/');
require_once MODX_CORE_PATH . 'model/modx/modx.class.php';

// Criteria for foreign Database
$host = 'localhost';
$username = 'your_username';
$password = 'your_password';
$dbname = 'your_database';
$port = 3306;
$charset = 'utf8';

$dsn = "mysql:host=$host;dbname=$dbname;port=$port;charset=$charset";
$xpdo = new xPDO($dsn, $username, $password);

// Test your connection
echo $o = ($xpdo->connect()) ? 'Connected' : 'Not Connected';

// Issue queries against the foreign database:
$results = $xpdo->query("SELECT id FROM some_table");
$recordCount = $results->rowCount();
print $recordCount;

Defining Multiple Connections (xPDO 2.2+)

xPDO 2.2 introduces the ability to define multiple connections, and includes configuration options for specifying read-only attributes per connection. This allows the use of xPDO with various kinds of master/slave database configurations. The feature is not meant to allow connecting to a specific database node, it is for configuring master/slave configurations where one (or more) nodes are read-only and at least one is writable (aka mutable). In that case you can request the initial connection be read-only and xPDO will automatically switch to a writable connection if a write operation is performed on a database object.


To define additional connections for an xPDO instance, you can pass an array of connection configuration arrays in the $options parameter of the xPDO constructor. Each connection array defines the same parameters as an xPDO constructor call. Here is an example constructor call with multiple read-only connections specified:

$xpdo = new xPDO('mysql:host=;dbname=xpdotest;charset=utf8', 'username', 'password' array(
    xPDO::OPT_CONN_MUTABLE => true,
    xPDO::OPT_CONN_INIT => array(xPDO::OPT_CONN_MUTABLE => false),
    xPDO::OPT_CONNECTIONS => array(
                'dsn' => 'mysql:host=;dbname=xpdotest;charset=utf8',
                'username' => 'username',
                'password' => 'password',
                'options' => array(
                    xPDO::OPT_CONN_MUTABLE => false,
                'driverOptions' => array(),
                'dsn' => 'mysql:host=;dbname=xpdotest;charset=utf8',
                'username' => 'username',
                'password' => 'password',
                'options' => array(
                    xPDO::OPT_CONN_MUTABLE => false,
                'driverOptions' => array(),


This option defines the mutability of a defined connection, i.e. is it a read-only connection or can we write to it. It can be specified in the $options array of the constructor as well as in the options for each additional connection.


This option defines criteria that a connection must meet to be considered for use as the initial connection created by xPDO. In master/slave configurations, a typical value for this option (which is specified only once in the main configuration options) would indicate to initialize a read-only or immutable connection.

xPDO::OPT_CONN_INIT => array(xPDO::_OPT_CONN_MUTABLE => false)

This makes sure that xPDO selects a connection with that option set to false to start with. If a write operation is performed within xPDO after a read-only connection is initialized, a new mutable connection will be selected and cached for reuse by other write operations within the same execution cycle.

See Also

The xPDO Constructor PDO::__construct()

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