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

This example shows us how we create one-to-one 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 test below.

Since this is a "composition" relationship, the child and parent should automatically be deleted if the one of them is deleted so you must add "remove" option to cascade attribute on the both entities otherwise removing one record will not remove record associated to it.

Mapping

Continent

declare(strict_types=1);

namespace App\Entity;

use Doctrine\ORM\Mapping as ORM;

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

    /**
     * @ORM\Column(name="name", type="string", length=100, nullable=false)
     */
    private $name;

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

    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 getCountry(): Country
    {
        return $this->country;
    }

    public function setCountry(Country $country): self
    {
        $this->country = $country;

        return $this;
    }
}

Country

declare(strict_types=1);

namespace App\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=100, nullable=false)
     */
    private $name;

    /**
     * @ORM\OneToOne(targetEntity="Continent", inversedBy="country", cascade={"persist", "remove"})
     * @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 getContinent(): Continent
    {
        return $this->continent;
    }

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

        return $this;
    }
}

Database

CREATE TABLE `continent` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(100) COLLATE utf8mb4_unicode_ci NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

CREATE TABLE `country` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `continent_id` int(11) NOT NULL,
  `name` varchar(100) COLLATE utf8mb4_unicode_ci NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `UNIQ_5373C966921F4C77` (`continent_id`),
  UNIQUE KEY `UNIQ_5373C9665E237E06` (`name`),
  CONSTRAINT `FK_5373C966921F4C77` FOREIGN KEY (`continent_id`) REFERENCES `continent` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

Test

Creating a new Continent and a new Country at same time.

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

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

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