* We use the "query by example" or QBE technique to retrieve the user by its email.
* We create an example object, populating its fields with the values we want matched,
* and sending the example object to the phpersistence query system.
* phpersistence will return the object that look like the example.
$example = new User();
$example->mail = "email@example.com";
// lets phpersistence do the job...
$persistence = new Persistence();
* findOneByExample returns one single element found by example.
* If the resultset is composed of more (or less) than 1 result, false is returned.
* If you want to get more than one result use findByExample (see next example)
$user = $persistence->findOneByExample($example) or die("phpersistence found more or less than 1 user");
// Logger::debug prints a dump of the object