Sometimes the handler might want us to use some kind of formula, so give it that option. If it wants us to do this, it must set $helper->formula = TRUE and implement handler->getFormula();
public function getField() {
if (!empty($this->formula)) {
return $this->handler
->getFormula();
}
else {
return $this->handler->tableAlias . '.' . $this->handler->realField;
}
}