How to Join Subqueries Using Doctrine 2 DBAL?

Join Subqueries with Doctrine 2 DBAL

In a Zend Framework 2 application, Zend_DB is being replaced with Doctrine 2.5 DBAL. The following Zend_DB query demonstrates this:

$subSelect = $db->select()
    ->from('user_survey_status_entries', array('userSurveyID', 'timestamp' => 'MIN(timestamp)'))
    ->where('status = ?', UserSurveyStatus::ACCESSED)
    ->group('userSurveyID');


$select = $db->select()
    // $selectColNames contains columns both from the main query and 
    // the subquery (e.g. firstAccess.timestamp AS dateFirstAccess).
    ->from(array('us' => 'user_surveys'), $selectColNames)
    ->joinLeft(array('firstAccess' => $subSelect), 'us.userSurveyID = firstAccess.userSurveyID', array())
    ->where('us.surveyID = ?', $surveyID);

However, users want to join the subquery using the Doctrine 2.5 query builder and select columns from the subquery in the main query. Unfortunately, Doctrine does not support joining subqueries.

Fortunately, users can use SQL query builder of Doctrine DBAL to write this query:

$subSelect = $connection->createQueryBuilder()
    ->select(array('userSurveyID', 'MIN(timestamp) timestamp'))
    ->from('user_survey_status_entries')
    // Instead of setting the parameter in the main query below, it could be quoted here:
    // ->where('status = ' . $connection->quote(UserSurveyStatus::ACCESSED))
    ->where('status = :status')
    ->groupBy('userSurveyID');

$select = $connection->createQueryBuilder()
    ->select($selectColNames)
    ->from('user_surveys', 'us')
    // Get raw subquery SQL and wrap in brackets.
    ->leftJoin('us', sprintf('(%s)', $subSelect->getSQL()), 'firstAccess', 'us.userSurveyID = firstAccess.userSurveyID')
    // Parameter used in subquery must be set in main query.
    ->setParameter('status', UserSurveyStatus::ACCESSED)
    ->where('us.surveyID = :surveyID')->setParameter('surveyID', $surveyID);

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