How to Join Subqueries in Doctrine 2 DBAL?

Join Subquery with Doctrine 2 DBAL

This article explores the process of joining subqueries in Doctrine 2. DBAL. While Doctrine 2 is known for not supporting subquery joins, this article presents a workaround using the DBAL connection's createQueryBuilder().

The preceding code can be adapted to use Doctrine 2 DBAL's query builder:

<code class="php">$subSelect = $connection->createQueryBuilder()
    ->select(array('userSurveyID', 'MIN(timestamp) timestamp'))
    ->from('user_survey_status_entries')
    ->where('status = :status')
    ->groupBy('userSurveyID');

$select = $connection->createQueryBuilder()
    ->select($selectColNames)
    ->from('user_surveys', 'us')
    ->leftJoin('us', sprintf('(%s)', $subSelect->getSQL()), 'firstAccess', 'us.userSurveyID = firstAccess.userSurveyID')
    ->setParameter('status', UserSurveyStatus::ACCESSED)
    ->where('us.surveyID = :surveyID')
    ->setParameter('surveyID', $surveyID);</code>

In this workaround, the subquery is constructed using createQueryBuilder() on the connection, not the entity manager, and its SQL is wrapped in brackets. It is then joined to the main query using leftJoin(), and the parameter used in the subquery is set in the main query using setParameter().

By following these steps, you can effectively join subqueries in Doctrine 2 DBAL, even though direct subquery support is not available.

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