inanzzz | One to many bidirectional composition example with Doctrine in Symfony

This example shows us how we create one-to-many composition relationship with Doctrine and Symfony.

Notes

Bidirectional: It provides navigational access in both directions.

Composition: As opposed to "aggregation" relationships, the child depends on the parent so the child exists only if the parent exists. You delete parent, the child is deleted too.

Design

Country is the "owning" side (relationship owner) and Continent is the "inverse" side.

The "owning" side uses the inversedBy attribute.

The "inverse" side uses the mappedBy attribute.

The nullable=false attribute on "owning" side enforces the composition relationship.

To prevent "A new entity was found through the relationship ..." exception while persisting an objects but not the other, we will add cascade={"persist"} attribute on both entities so this is a precautionary measure. It will also help us not calling persist on a new child object where possible. You will see in the tests below.

Since this is a "composition" relationship, the child should automatically be deleted if the parent is deleted so you must add "remove" option to cascade attribute on the parent entity which is "Continent" otherwise trying to remove a parent record would throw an exception if there is a child record associated to it.

Mapping

Continent

declare(strict_types=1);

namespace AppBundle\Entity;

use Doctrine\Common\Collections\ArrayCollection;
use Doctrine\Common\Collections\Collection;
use Doctrine\ORM\Mapping as ORM;

/**
 * @ORM\Entity
 * @ORM\Table(name="continent", uniqueConstraints={@ORM\UniqueConstraint(columns={"name"})})
 */
class Continent
{
    /**
     * @ORM\Id
     * @ORM\Column(name="id", type="integer")
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    private $id;

    /**
     * @ORM\Column(name="name", type="string", length=13, nullable=false)
     */
    private $name;

    /**
     * @ORM\OneToMany(targetEntity="Country", mappedBy="continent", cascade={"persist", "remove"})
     */
    private $countries;

    public function __construct()
    {
        $this->countries = new ArrayCollection();
    }

    public function getId(): int
    {
        return $this->id;
    }

    public function setName(string $name): self
    {
        $this->name = $name;

        return $this;
    }

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

    public function addCountry(Country $country): self
    {
        $this->countries[] = $country;

        return $this;
    }

    public function removeCountry(Country $country): bool
    {
        return $this->countries->removeElement($country);
    }

    public function getCountries(): Collection
    {
        return $this->countries;
    }
}

Country

declare(strict_types=1);

namespace AppBundle\Entity;

use Doctrine\ORM\Mapping as ORM;

/**
 * @ORM\Entity
 * @ORM\Table(name="country", uniqueConstraints={@ORM\UniqueConstraint(columns={"name"})})
 */
class Country
{
    /**
     * @ORM\Id
     * @ORM\Column(name="id", type="integer")
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    private $id;

    /**
     * @ORM\Column(name="name", type="string", length=13, nullable=false)
     */
    private $name;

    /**
     * @ORM\ManyToOne(targetEntity="Continent", inversedBy="countries", cascade={"persist"})
     * @ORM\JoinColumn(name="continent_id", referencedColumnName="id", nullable=false)
     */
    private $continent;

    public function getId(): int
    {
        return $this->id;
    }

    public function setName(string $name): self
    {
        $this->name = $name;

        return $this;
    }

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

    public function setContinent(Continent $continent): self
    {
        $this->continent = $continent;

        return $this;
    }

    public function getContinent(): Continent
    {
        return $this->continent;
    }
}

Database

CREATE TABLE `continent` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(13) COLLATE utf8_unicode_ci NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `UNIQ_6CC70C7C5E237E06` (`name`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

CREATE TABLE `country` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `continent_id` int(11) NOT NULL,
  `name` varchar(13) COLLATE utf8_unicode_ci NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `UNIQ_5373C9665E237E06` (`name`),
  KEY `IDX_5373C966921F4C77` (`continent_id`),
  CONSTRAINT `FK_5373C966921F4C77` FOREIGN KEY (`continent_id`) REFERENCES `continent` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

Tests

Create a new Continent.

$continent = new Continent();
$continent->setName('Africa');

$this->entityManager->persist($continent);
$this->entityManager->flush();

Create a new Continent and Country at same time.

$country = new Country();
$country->setName('Gana');

$continent = new Continent();
$continent->setName('Africa');

$country->setContinent($continent);
$continent->addCountry($country);

// You can use both of them at same time but using one over another is more logical as cascade={"persist"} will handle it for us.
$this->entityManager->persist($continent);
$this->entityManager->persist($country);
//

$this->entityManager->flush();

Creating a new Country.

/** @var Continent $continent */
$continent = $this->entityManager->getRepository(Continent::class)->findOneById(1);

$country = new Country();
$country->setName('Gana');
$country->setContinent($continent);

// You can use both of them at same time but using one over another is more logical as cascade={"persist"} will handle it for us.
$continent->addCountry($country);
$this->entityManager->persist($country);
//

$this->entityManager->flush();