Why does a Element Criteria Model Query with Strings on a custom element type not filtering?

Question

having issues doing the classic element type query, works fine with numerical criteria (id, price etc.) but fails on strings, (code, name etc.). It just returns all elements.

$criteria = craft()->elements->getCriteria('GoWander_Trip');
$criteria->code = $code;
return $criteria->find();

Is there any step im missing in the setup of the element itself (code below)?

public function modifyElementsQuery(DbCommand $query, ElementCriteriaModel $criteria) {

    $query
        ->addSelect('
            trips.code, 
            trips.templateId, 
            trips.start, 
            trips.end, 
            trips.assetId, 
            trips.price, 
            trips.spots, 
            trips.spotsAvailable,
            trips.elements,
            trips.shortDescription
        ')
        ->join('gowander_trips trips', 'trips.id = elements.id');

    if ($criteria->templateId) {

        $query->andWhere(DbHelper::parseParam('trips.templateId', $criteria->templateId, $query->params));
    }

}

Answer 1

Found the answer, simple mistake.

if ($criteria->code) {
   $query->andWhere(DbHelper::parseParam('trips.code', $criteria->code, $query->params));
}

was needed along with

public function defineCriteriaAttributes() {

    return array(
        'templateId'    => AttributeType::Mixed,
        'code'          => AttributeType::String,
    );
}

Hopes that helps anyone else who comes across something like this.