Doctrine2 DBAL Exists query - mysql

Question

I would like to ask for your help with Doctrine2 DBAL query built with QueryBuilder. I'm used to ORM, but I think it's an overkill for such query which is being called in a listener.
I need a query with SELECT EXISTS and I don't know how I can construct it using DBAL QueryBuilder.
I have a subquery already created:
$subQuery = $connection->createQueryBuilder();
$subQuery
->select('o.id')
->from('order', 'o')
->leftJoin('o', 'payment', 'p')
->where($subQuery->expr()->isNull('p.id'))
;
I basically want to check if there are any unpaid orders. I now have no idea how to build the SELECT EXISTS query? Can anyone point me in the right direction? I was thinking about something like this:
$qb->select('EXISTS(?)')->setParameter($subQuery->getDQL())
Will that be the correct solution?
#EDIT
After a while of thinking I decided to use ORM instead. Unfortunately that did not work either, I'm getting an error:
line 0, col 7: Error: Expected known function, got 'EXISTS'
The DQL is:
SELECT EXISTS(<subquery here>)
It is a bit weird considering that It has been build with QueryBuilder:
/* #var $qb QueryBuilder */
$qb = $this->em->createQueryBuilder();
$qb
->select($qb->expr()->exists($subQuery->getDQL()));

Answer 1

A few years late, but you need to specify your EXISTS subquery SQL within the SELECT or WHERE statement portion of the QueryBuilder, as opposed to using a parameter.
Additionally since order is a reserved word in MySQL, you will need to use identifier quotes ` (back-tick) to escape the table name.
When using the ORM; you must specify a FROM statement that references an entity, so you would need to change your approach.
$connection = $this->em->getConnection();
$expr = $connection->getExpressionBuilder();
$qbSub = $connection->createQueryBuilder()
->select('1')
->from('`order`', 'o')
->leftJoin('o', '`payment`', 'p', $expr->eq('p.order_id', 'o.id'))
->where($expr->isNull('p.id'));
/**
* #return string "1" if a record exists, "0" otherwise
*/
$connection->createQueryBuilder()
->select('EXISTS(' . $qbSub->getSQL() . ')')
->execute()
->fetchColumn();
Resulting SQL
SELECT EXISTS(
SELECT 1
FROM `order` AS o
LEFT JOIN `payment` AS p
ON p.order_id = o.id
WHERE p.id IS NULL
);
Note: If you have any parameters, the values for the placeholders must be bound using QueryBuilder::setParameter() on the top-level
query, not the sub-queries.
$qbSub = $connection->createQueryBuilder()
->select('1')
->from('`order`', 'o')
->leftJoin('o', '`payment`', 'p', $expr->andX(
$expr->eq('p.order_id', 'o.id'),
$expr->eq('p.name', ':name') // subquery placeholder
))
->where($expr->isNull('p.id'));
$connection->createQueryBuilder()
->select('EXISTS(' . $qbSub->getSQL() . ')')
->setParameter('name', $value) // subquery placeholder param value
->execute()
->fetchColumn();
However, I suggest changing your query from an exclusion join to an inclusion join with NOT EXISTS. Doing so will filter orders that have been paid, out of your result-set. Instead of attempting to join every order on every payment and retrieve the payments that return null. Dramatically improving the performance of the query.
Example db-fiddle
SELECT EXISTS (
SELECT 1
FROM `order` AS o
WHERE NOT EXISTS(
SELECT NULL
FROM `payment` AS p
WHERE p.order_id = o.id
)
)