mapping.php

<?php

$column = new Column("email", Type::getType("string"));

$column->setLength(255);
$column->setNullable(true);

$classMetadata->getTable()->addColumn($column);

$value = new SimpleValue();

$value->setTable($classMetadata->getTable());
$value->setTypeName("string");
$value->addColumn($column);

$property = new Property("email");

$property->setValue($value);

$classMetadata->addProperty($property);