doctrine / orm

            $indexByProperty  = $targetClass->getProperty($indexBy);

            switch (true) {

                case ($indexByProperty instanceof FieldMetadata):

                    $quotedColumnName = $this->platform->quoteIdentifier($indexByProperty->getColumnName());

                    $whereClauses[] = sprintf('tr.%s = ?', $quotedColumnName);

                    $params[]       = $key;

                    $types[]        = $indexByProperty->getType();

                    break;

                case ($indexByProperty instanceof ToOneAssociationMetadata && $indexByProperty->isOwningSide()):

                    // Cannot be supported because PHP does not accept objects as keys. =(

            $property = $this->class->getProperty($idField);

            switch (true) {

                case ($property instanceof FieldMetadata):

                    $where[]  = $this->platform->quoteIdentifier($property->getColumnName());

                    $params[] = $identifier[$idField];

                    $types[]  = $property->getType();

                    break;

                case ($property instanceof ToOneAssociationMetadata):

                    $targetClass = $this->em->getClassMetadata($property->getTargetEntity());