Join from inversed side - symfony

Question

given the two following intities:
<?php
/**
* User
* #ORM\Entity()
*/
class User implements AdvancedUserInterface, \Serializable, EncoderAwareInterface
{
/**
* #var Vip
* #ORM\OneToOne(targetEntity="Vip", mappedBy="user", fetch="EAGER")
*/
protected $vip;
// …
<?php
/**
* Vip
* #ORM\Entity()
*/
class Vip
{
/**
* #ORM\id #ORM\OneToOne(targetEntity="User", inversedBy="vip", fetch="EAGER")
* #ORM\JoinColumn(name="user_id", referencedColumnName="id", nullable=false)
*/
protected $user;
// …
SHORT :
How can I do this SQL in DQL given above entities:
SELECT u.firstName, v.foo FROM User join Vip v ON v.user_id = u.id
In other words how can I retrieve 10 first users ( with their VIP infos if it exists), using DQL join in such a way that only one SQL query will be generated by Doctrine. Is that possible ?
Long story:
The owning side is the Vip entity because it holds the reference/foreign key to a User underneath in the database.
I am trying to retrieve all User with their Vip datas.
Using the knplabs/knp-paginator-bundle, I first set up a simple query:
$dql = "SELECT u, p FROM AppBundle:User u;
In spite of enforcing the fetch attribute as « EAGER », Vip infos where not part of the initial query. As a consequence, calling getter getVip() on each iteration from inside the twig for in loop like
{% for user in pagination %}
{% if user.getVip() %}
<span class="label label-warning">V.I.P</span>
{% endif %}
{{% endfor %}}
.. caused a query to be issued on each iteration !
The Symfony dev bar shows 6 queries:
DQL documentation and says that one can use JOIN keyword. So my query became:
$dql = "SELECT u, v FROM AppBundle:User u JOIN u.vip v;
But now I get this error:
Warning: spl_object_hash() expects parameter 1 to be object, null
given
Here I'm stuck, wondering how I could fetch Vip datas (or null) along with User datas, in a single query.

Answer 1

In other words how can I retrieve 10 first users ( with their VIP
infos if it exists), using DQL join in such a way that only one SQL
query will be generated by Doctrine. Is that possible ?
You should initialize all related entities using select clause to avoid additional queries when accessing to the related objects.
$repository = $em->getRepository(User::class);
$users = $repository->createQueryBuilder('u')
->addSelect('v') // Initialize Vip's
->join('u.vip', 'v')
->getQuery()
->setMaxResults(10)
->getResult();

Answer 2

Yes, one may add associated entities to the SELECT statement.
But more precisely, one should only add relations that are really involved in the expected result , in other words, entities fetched as "EAGER".
I realized that the vip entity had another relation (oneToMany with a vehicule entity). I just want to retrieve users with their vip metas. Adding another JOIN to the query would just bring more datas since I would not use vehicules anyway (and issue extra work behind the scenes).
-> So I simply changed the fetch attribute from "EAGER" to "LAZY" in the vip OneToMany declaration.
To conclude:
Ask yourself «what are involved intities ?», should it be part
of the result (do you simply need those infos).
if NO, you might turn fetch attribute to "[EXTRA_]LAZY" in the relation declaration like
/**
* #ORM\OneToMany(targetEntity="Vehicule", mappedBy="vip", fetch="LAZY", …)
*/
protected $vehicules;
if YES you will have to select those entities in your query.
Using DQL:
SELECT u, v, w FROM AppBundle:User u LEFT JOIN u.vip v LEFT JOIN v.vehicules w
Using queryBuilder:
$repository = $em->getRepository(User::class);
$users = $repository->createQueryBuilder('u')
->addSelect('v')
->join('u.vip', 'v')
->addSelect('w')
->join('v.vehicules', 'w')
// …