Question

Here is Database.php:

<?php
/*Data Base Class
* MySQL - InnoDB 
* PHP - PDO (PHP Data Object -So we could change databases if needed)
*/
class Database extends PDO{
    private $DBH;

    function __construct($host, $dbname, $user, $pass){
        try {
            $this->DBH = new PDO("mysql:host=$host;dbname=$dbname", $user, $pass);
        } catch (PDOException $e) {  
            return $e->getMessage();  
        }
    }

    public function alteration_query($sql){
        /* Begin a transaction, turning off autocommit */
        $this->DBH->beginTransaction();
        try{
            $count = $this->DBH->exec($sql);
            $this->DBH->commit();
            return $count;
        }catch (PDOException $e) {
          $this->DBH->rollback();
          return  $e;
        }
    }
}
?>

Here is test.php:

<?php
require('Database.php');
$dbo = new Database('***.***.com','***','***','***');
echo $dbo->alteration_query('DELETE * from T_Table');
?>

For some reason, it won’t give me an error or delete the contents of the T_table.

Answer 1

EDIT: The problem in your case is that the argument is called $sql, but you’re using $query to execute it (in the alteration_query method). Next time, please enable error reporting, and/or use a decent IDE, that can show you these errors. Like so:

EDIT2: Set PDO’s error mode to exception, this way any error would throw an exception. See updated code.

Don’t catch your exceptions inside of the functions, do it outside:

<?php
/*Data Base Class
* MySQL - InnoDB 
* PHP - PDO (PHP Data Object -So we could change databases if needed)
*/
class Database
{
    private $DBH;

    function __construct($host, $dbname, $user, $pass)
    {
        $this->DBH = new PDO("mysql:host=$host;dbname=$dbname", $user, $pass);
        //Set PDO to throw exceptions on errors!
        $this->DBH->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    }

    public function alteration_query($sql)
    {
        /* Begin a transaction, turning off autocommit */
        $this->DBH->beginTransaction();
        $count = $this->DBH->exec($query);
        $this->DBH->commit();
        return $count;
    }
}

try {
    $pdo = new Database("localhost", "dbname", "user", "pass");
    $pdo->alteration_query("SELECT * FROM wrong_table");
}
catch (PDOException $e) {
    die("An error has occured! " . $e->getMessage());
}

This way, you can catch the error exactly where you need it, and not force it inside of the function (which kinda beats the point of the exception).

Also, from the manual:

When the script ends or when a connection is about to be closed, if
you have an outstanding transaction, PDO will automatically roll it
back. This is a safety measure to help avoid inconsistency in the
cases where the script terminates unexpectedly–if you didn’t
explicitly commit the transaction, then it is assumed that something
went awry, so the rollback is performed for the safety of your data.

Exceptions halt the execution of the function, meaning the commit() never happens, and it rolls back.