What does ':'(colon) mean in dql?

Question

I'm working on a server that uses doctrine orm, and i came across the following function:

public function showForJustWhoCanSee() {
        $subquery = $this->em->createQueryBuilder();
        $subquery->select('userSignature')
            ->from('HospitalApi\Entity\EletronicDocumentSignature', 'signature')
            ->innerJoin('HospitalApi\Entity\User', 'userSignature', 'WITH', 'userSignature = signature.user')
            //->where('signature.signed = 0')
            ->groupBy('signature._document')
            ->orderBy('signature.order', 'ASC');

        $select = $this->em->createQueryBuilder();
        $select->select('ed')
            ->from($this->getEntityPath(), 'ed')
            ->innerJoin("HospitalApi\Entity\User", "u", "with", "ed.user = u")
            ->leftJoin("HospitalApi\Entity\EletronicDocumentSignature", 'eds', 'WITH', 'eds._document = ed')
            ->leftJoin("eds.user", 'us', 'WITH', 'u = :user OR us = :user')
            ->where( $select->expr()->eq( 'us', $select->expr()->any( $subquery->getDQL() )) )
            // ->andwhere('eds.signed = 0')
            // ->andwhere( $select->expr()->in('ed.status', $this->_alowedStatusToSign) )
            ->orwhere('u = :user')
            ->setParameter('user', $this->getSession() )
            ->andWhere('ed.c_removed = 0');
        return $select;
    }

I would like to know what the colon on ':user' does at:

->leftJoin("eds.user", 'us', 'WITH', 'u = :user OR us = :user')

Thanks in advance.

Answer 1

The colon is used in parameter binding... you define a name: :user

And then you assign a value to that parameter in:

->setParameter('user', $this->getSession() )