ONE task can have MULTIPLE tags, ONE tag can apply to MULTIPLE tasks – the CLASSIC many-to-many relationship, EXACTLY as in the Symfony course (chapter 32).

The tags property on Task

use Doctrine\Common\Collections\ArrayCollection;
use Doctrine\Common\Collections\Collection;

// ... inside the class:

#[ORM\ManyToMany(targetEntity: Tag::class, inversedBy: 'tasks')]
#[Groups(['task:read', 'task:write'])]
private Collection $tags;

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

public function getTags(): Collection
{
    return $this->tags;
}

public function addTag(Tag $tag): static
{
    if (!$this->tags->contains($tag)) {
        $this->tags->add($tag);
    }

    return $this;
}

public function removeTag(Tag $tag): static
{
    $this->tags->removeElement($tag);

    return $this;
}

The inverse side on Tag

use Doctrine\Common\Collections\ArrayCollection;
use Doctrine\Common\Collections\Collection;

// ... inside the class:

#[ORM\ManyToMany(targetEntity: Task::class, mappedBy: 'tags')]
private Collection $tasks;

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

DELIBERATELY WITHOUT #[Groups] on tasks – Tag has been read-only since chapter 12 and doesn't NEED to show its related tasks in the API response to make the relationship USABLE.

Creating a migration

docker compose exec php bin/console make:migration
docker compose exec php bin/console doctrine:migrations:migrate --no-interaction

CREATES an ADDITIONAL join table (task_tag) – EXACTLY the USUAL database pattern for many-to-many relationships, FULLY managed by Doctrine.

Creating a task with tags

curl -k -X POST https://localhost/api/tasks \
  -H 'Content-Type: application/json' \
  -d '{"title": "Prepare deployment", "project": "/api/projects/1", "tags": ["/api/tags/1", "/api/tags/2"]}'

tags as an ARRAY of IRIs – EXACTLY the same principle as the SINGLE project field, just PLURAL for a many-to-many relationship.