Is it possible to use result of an SQL function as a field in Doctrine?

Question

Assume I have Product entities and Review entities attached to products. Is it possible to attach a fields to a Product entity based o

Answer 1

After detailed investigation I've found there are several ways to do something close to what I wanted including listed in other answers, but all of them have some minuses. Finally I've decided to use CustomHydrators. It seems that properties not managed with ORM cannot be mapped with ResultSetMapping as fields, but can be got as scalars and attached to an entity manually (as PHP allows to attach object properties on the fly). However, result that you get from doctrine remains in the cache. That means properties set in that way may be reset if you make some other query that would contain these entities too.

Another way to do that was adding these field directly to doctrine's metadata cache. I tried doing that in a CustomHydrator:

protected function getClassMetadata($className)
{
    if ( ! isset($this->_metadataCache[$className])) {
        $this->_metadataCache[$className] = $this->_em->getClassMetadata($className);

        if ($className === "SomeBundle\Entity\Product") {
            $this->insertField($className, "ReviewsCount");
        }
    }

    return $this->_metadataCache[$className];
}

protected function insertField($className, $fieldName) {
    $this->_metadataCache[$className]->fieldMappings[$fieldName] = ["fieldName" => $fieldName, "type" => "text", "scale" => 0, "length" => null, "unique" => false, "nullable" => true, "precision" => 0];
    $this->_metadataCache[$className]->reflFields[$fieldName] = new \ReflectionProperty($className, $fieldName);

    return $this->_metadataCache[$className];
}

However, that method also had problems with entities' properties reset. So, my final solution was just to use stdClass to get the same structure, but not managed by doctrine:

namespace SomeBundle;

use PDO;
use Doctrine\ORM\Query\ResultSetMapping;

class CustomHydrator extends \Doctrine\ORM\Internal\Hydration\ObjectHydrator {
    public function hydrateAll($stmt, $resultSetMapping, array $hints = array()) {
        $data = $stmt->fetchAll(PDO::FETCH_ASSOC);

        $result = [];

        foreach($resultSetMapping->entityMappings as $root => $something) {
            $rootIDField = $this->getIDFieldName($root, $resultSetMapping);

            foreach($data as $row) {
                $key = $this->findEntityByID($result, $row[$rootIDField]);

                if ($key === null) {
                    $result[] = new \stdClass();
                    end($result);
                    $key = key($result);
                }

                foreach ($row as $column => $field)
                    if (isset($resultSetMapping->columnOwnerMap[$column]))
                        $this->attach($result[$key], $field, $this->getPath($root, $resultSetMapping, $column));
            }
        }


        return $result;
    }

    private function getIDFieldName($entityAlias, ResultSetMapping $rsm) {
        foreach ($rsm->fieldMappings as $key => $field)
            if ($field === 'ID' && $rsm->columnOwnerMap[$key] === $entityAlias) return $key;

            return null;
    }

    private function findEntityByID($array, $ID) {
        foreach($array as $index => $entity)
            if (isset($entity->ID) && $entity->ID === $ID) return $index;

        return null;
    }

    private function getPath($root, ResultSetMapping $rsm, $column) {
        $path = [$rsm->fieldMappings[$column]];
        if ($rsm->columnOwnerMap[$column] !== $root) 
            array_splice($path, 0, 0, $this->getParent($root, $rsm, $rsm->columnOwnerMap[$column]));

        return $path;
    }

    private function getParent($root, ResultSetMapping $rsm, $entityAlias) {
        $path = [];
        if (isset($rsm->parentAliasMap[$entityAlias])) {
            $path[] = $rsm->relationMap[$entityAlias];
            array_splice($path, 0, 0, $this->getParent($root, $rsm, array_search($rsm->parentAliasMap[$entityAlias], $rsm->relationMap)));
        }

        return $path;
    }

    private function attach($object, $field, $place) {
        if (count($place) > 1) {
            $prop = $place[0];
            array_splice($place, 0, 1);
            if (!isset($object->{$prop})) $object->{$prop} = new \stdClass();
            $this->attach($object->{$prop}, $field, $place);
        } else {
            $prop = $place[0];
            $object->{$prop} = $field;
        }
    }
}

With that class you can get any structure and attach any entities however you like:

$sql = '
    SELECT p.*, COUNT(r.id)
    FROM products p
    LEFT JOIN reviews r ON p.id = r.product_id
';

$em = $this->getDoctrine()->getManager();

$rsm = new ResultSetMapping();
$rsm->addEntityResult('SomeBundle\Entity\Product', 'p');
$rsm->addFieldResult('p', 'COUNT(id)', 'reviewsCount');

$query = $em->createNativeQuery($sql, $rsm);

$em->getConfiguration()->addCustomHydrationMode('CustomHydrator', 'SomeBundle\CustomHydrator');
$results = $query->getResult('CustomHydrator');

Hope that may help someone :)