How can I refactor/ simplify the following php function?

Question

I have a function that will return how many products there are on an invoice and it seems pretty straightforward to me but maybe it can use some refactoring?

    public function getTotalProductsNumber(): int
{
    $dataset = 'supplier_invoice_products inner join supplier_invoices as si using (supplier_invoice_id)';
    $dbmSupplier = new Dbm_Supplier($dataset);

    $whereAndOpt = $this->getConditionsAndOptions();
    $where = $whereAndOpt['where'];
    $opt = $whereAndOpt['opt'];
    $select = 'sum(product_quantity) as sumTotal';
    $invoiceTotalProductsNumber =  $dbmSupplier->findFirstSimple($where, $select, $opt);
    $invoiceTotalProductsNumber['sumTotal'] = (int)$invoiceTotalProductsNumber['sumTotal'];
    return $invoiceTotalProductsNumber['sumTotal'];
}

How can I extract this into at least two functions?

Answer 1

For this kind of thing, ideally you'd use an ORM. As I'm not sure which you're using, if at all, I'd probably refactor it to something more in this direction so it feels closer to how an ORM would work:

public function getTotalProductsNumber(): int
{
    $dataset = 'supplier_invoice_products inner join supplier_invoices as si using (supplier_invoice_id)';
    $extras = $this->getConditionsAndOptions();
    $queryBuilder = [
        'dbm' => new Dbm_Supplier($dataset),
        'where' =>  $extras['where'],
        'opt' => $extras['opt']
    ];
    return $this->sumOfProductQuantities($queryBuilder);
}

private function sumOfProductQuantities(array $queryBuilder): int
{
    $select = 'sum(product_quantity) as sumTotal';
    $row = $this->queryBuilderFirstRow($queryBuilder, $select);
    return (int)$row['sumTotal'];
}

private function queryBuilderFirstRow(array $qb, string $select): array
{
    return $qb['dbm']->findFirstSimple($qb['where'], $select, $qb['opt']);
}