Question

I have a Car entity with a many-to-one relationship with an entity Owner. If I select all cars, Doctrine does one query on the Car table, and subsequently one query on the Owner table for each car. So fetching N cars becomes N+1 queries instead of a single JOIN query between the Car and Owner tables.

My entities are as follows:

/** @Entity */
class Car {

  /** @Id @Column(type="smallint") */
  private $id;

  /** @ManyToOne(targetEntity="Owner", fetch="EAGER")
      @JoinColumn(name="owner", referencedColumnName="id") */
  private $owner;

  public function getId()    { return $this->id; }
  public function getOwner() { return $this->owner; }
}

/** @Entity */
class Owner {

  /** @Id @Column(type="smallint") */
  private $id;

  /** @Column(type="string") */
  private $name;

  public function getName() { return $this->name; }
}

If I want to list the cars with their owners, I do:

$repo = $em->getRepository('Car');
$cars = $repo->findAll();

foreach($cars as $car) 
  echo 'Car no. ' . $car->getId() . 
       ' owned by ' . $car->getOwner()->getName() . '\n';

Now this all works very well, apart from the fact that Doctrine issues a query for each car.

SELECT * FROM Car;
SELECT * FROM Owner WHERE id = 1;
SELECT * FROM Owner WHERE id = 2;
SELECT * FROM Owner WHERE id = 3;
....

Of course I’d want my query log to look like this:

SELECT * FROM Car JOIN Owner ON Car.owner = Owner.id;

Whether I have fetch="EAGER" or fetch="LAZY" doesn’t matter, and even if I make a custom DQL query with JOIN between the two entities, $car->getOwner() still causes Doctrine to query the database (unless I use EAGER, in which case $repo->findAll() causes all of them).

Am I just too tired here, and this is the way it is supposed to work – or is there a clever way to force Doctrine to do the JOIN query instead?

Answer 1

At least in 1.x Doctrine if you wanted to query for the related objects, you had to use DQL. For your case, the DQL query would look something like this:

//Assuming $em is EntityManager
$query = $em->createQuery('SELECT c, o FROM Car c JOIN c.owner o');
$cars = $query->execute();