Today, a friend asking me if it was possible to get a prepared statement back from PDO with the values placeholders replaced, finally caught me in a moment where I could do something about it.

I wrote a thin PDO wrapper class that will [imperfectly, I'm sure] return the completed query.

It supports bound parameters, values and the array key->value methods of passing in values to prepared queries. You can see the code and examples below:

<?php
class PDOTester extends PDO {
	public function __construct($dsn, $username = null, $password = null, $driver_options = array())
	{
		parent::__construct($dsn, $username, $password, $driver_options);
		$this->setAttribute(PDO::ATTR_STATEMENT_CLASS, array('PDOStatementTester', array($this)));
	}
}

class PDOStatementTester extends PDOStatement {
	const NO_MAX_LENGTH = -1;

	protected $connection;
	protected $bound_params = array();

	protected function __construct(PDO $connection)
	{
		$this->connection = $connection;
	}

	public function bindParam($paramno, &$param, $type = PDO::PARAM_STR, $maxlen = null, $driverdata = null)
	{
		$this->bound_params[$paramno] = array(
			'value' => &$param,
			'type' => $type,
			'maxlen' => (is_null($maxlen)) ? self::NO_MAX_LENGTH : $maxlen,
			// ignore driver data
		);

		$result = parent::bindParam($paramno, $param, $type, $maxlen, $driverdata);
	}

	public function bindValue($parameter, $value, $data_type = PDO::PARAM_STR)
	{
		$this->bound_params[$parameter] = array(
			'value' => $value,
			'type' => $data_type,
			'maxlen' => self::NO_MAX_LENGTH
		);
		parent::bindValue($parameter, $value, $data_type);
	}

	public function getSQL($values = array())
	{
		$sql = $this->queryString;

		if (sizeof($values) > 0) {
			foreach ($values as $key => $value) {
				$sql = str_replace($key, $this->connection->quote($value), $sql);
			}
		}

		if (sizeof($this->bound_params)) {
			foreach ($this->bound_params as $key => $param) {
				$value = $param['value'];
				if (!is_null($param['type'])) {
					$value = self::cast($value, $param['type']);
				}
				if ($param['maxlen'] && $param['maxlen'] != self::NO_MAX_LENGTH) {
					$value = self::truncate($value, $param['maxlen']);
				}
				if (!is_null($value)) {
					$sql = str_replace($key, $this->connection->quote($value), $sql);
				} else {
					$sql = str_replace($key, 'NULL', $sql);
				}
			}
		}
		return $sql;
	}

	static protected function cast($value, $type)
	{
		switch ($type) {
			case PDO::PARAM_BOOL:
				return (bool) $value;
				break;
			case PDO::PARAM_NULL:
				return null;
				break;
			case PDO::PARAM_INT:
				return (int) $value;
			case PDO::PARAM_STR:
			default:
				return $value;
		}
	}

	static protected function truncate($value, $length)
	{
		return substr($value, 0, $length);
	}
}

$pdo = new PDOTester('sqlite::memory:');
$pdo->query('CREATE TABLE foo (bar TEXT, baz TEXT, num NUMERIC, empty TEXT)');
$query = $pdo->prepare('SELECT * FROM foo WHERE bar = :bar AND baz = :baz');

// Test with passed in array
echo $query->getSQL(array(':bar' => 'foo', ':baz' => 'bat')) . PHP_EOL;

$query = $pdo->prepare('SELECT * FROM foo WHERE bar = :bar AND baz = :baz AND num = :num AND empty=:empty');

// Test with bound params and values
$bar = 'bar';
$baz = 'baz';
$num = '0.1';
$empty = 'empty!!';

// Bind Param
$query->bindParam(':bar', $bar);

// Bind Value
$query->bindValue(':baz', $baz);

// Bind With types
$query->bindParam(':num', $num, PDO::PARAM_INT);
$query->bindParam(':empty', $empty, PDO::PARAM_NULL);

echo $query->getSQL() . PHP_EOL;

// Change the vars
$bar = 'foo';
$baz = 'bat';
$num = '2.6';
$empty = 'blah!';

echo $query->getSQL() . PHP_EOL;

// Bind with length
$query->bindParam(':bar', $bar, PDO::PARAM_STR, 2);

echo $query->getSQL() . PHP_EOL;
?>

This results in the following output:

SELECT * FROM foo WHERE bar = 'foo' AND baz = 'bat'
SELECT * FROM foo WHERE bar = 'bar' AND baz = 'baz' AND num = '0' AND empty=NULL
SELECT * FROM foo WHERE bar = 'foo' AND baz = 'baz' AND num = '2' AND empty=NULL
SELECT * FROM foo WHERE bar = 'fo' AND baz = 'baz' AND num = '2' AND empty=NULL

Hopefully, this will help you get a somewhat better idea of what’s going on

- Davey