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Pagination
Doctrine ORM ships with a Paginator for DQL queries. It
has a very simple API and implements the SPL interfaces Countable and
IteratorAggregate.
<?phpuse Doctrine\ORM\Tools\Pagination\Paginator;$dql = "SELECT p, c FROM BlogPost p JOIN p.comments c";$query = $entityManager->createQuery($dql) ->setFirstResult(0) ->setMaxResults(100);$paginator = new Paginator($query, fetchJoinCollection: true);$c = count($paginator);foreach ($paginator as $post) { echo $post->getHeadline() . "\n";}Paginating Doctrine queries is not as simple as you might think in the beginning. If you have complex fetch-join scenarios with one-to-many or many-to-many associations using the "default" LIMIT functionality of database vendors is not sufficient to get the correct results.
By default the pagination extension does the following steps to compute the correct result:
- Perform a Count query using
DISTINCTkeyword. - Perform a Limit Subquery with
DISTINCTto find all ids of the entity in from on the current page. - Perform a WHERE IN query to get all results for the current page.
This behavior is only necessary if you actually fetch join a to-many
collection. You can disable this behavior by setting the
fetchJoinCollection argument to false; in that case only 2 instead of the 3 queries
described are executed. We hope to automate the detection for this in
the future.
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By using the Paginator::HINT_ENABLE_DISTINCT you can instruct doctrine that the query to be executed
will not produce "duplicate" rows (only to-one relations are joined), thus the SQL limit will work as expected.
In this way the DISTINCT keyword will be omitted and can bring important performance improvements.
<?phpuse Doctrine\ORM\Tools\Pagination\Paginator;$dql = "SELECT u, p FROM User u JOIN u.mainPicture p";$query = $entityManager->createQuery($dql) ->setHint(Paginator::HINT_ENABLE_DISTINCT, false) ->setFirstResult(0) ->setMaxResults(100);