Persisting Doctrine Entity with Collection results in exception

Question

Am working on a simple setup with two tables with a one to many (and inversed) relationship. The two corresponding entities are:

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

/**
 * @ORM\Entity(repositoryClass=ArticlesRepository::class)
 * @ORM\Table(name="articles")
 */
class Article
{

    /**
     * @ORM\Id
     * @ORM\GeneratedValue
     * @ORM\Column(name="unique_id", type="integer")
     */
    protected int $idx;

    /**
     * The inverse side
     * @ORM\OneToMany(targetEntity="Comment", mappedBy="article")
     * @ORM\Column(name="uid", type="integer", nullable=true)
     */
    protected $id;

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

and

use Doctrine\ORM\Mapping as ORM;

/**
 * ORM\Entity(repositoryClass="CommentRepository::class")
 * ORM\Table(name="comments")
 */
class Comment 
{

    /**
     * @ORM\Id
     * @ORM\GeneratedValue
     * @ORM\Column(name="uid", type="integer")
     */
    protected $idx;

    /**
     * The owning side
     * @ORM\ManyToOne(targetEntity="Article", inversedBy="uid")
     * @ORM\JoinColumn(name="article", referencedColumnName="uid")
     */
    protected $article;

    protected $content;
}

Attempting to persist a new blank Article

        $article=new Article();
        $em->persist($article);
        $em->flush();

results in the following exception

An exception occurred while executing 'INSERT INTO articles (uid) VALUES (?)' with params [{}]: PHP Warning: Object of class Doctrine\Common\Collections\ArrayCollection could not be converted to float in ...\vendor\doctrine\dbal\lib\Doctrine\DBAL\Driver\Mysqli\MysqliStatement.php line 164

I went searching for answers and came across suggestions close to but don't touch on this subject. One had to do with removing the type indication of the column. So I did and it gets stuck with the following exception

An exception occurred while executing 'INSERT INTO articles (uid) VALUES (?)' with params [{}]: Cannot add or update a child row: a foreign key constraint fails...

When type is removed, the field defaults to type string which makes no difference, since Doctrine still attempts to store an empty array in an integer field (see the values in the exception above).

Question: How can I get the setup to work properly and persist all objects correctly?

Answer 1

It turns out that the @ORM\OneToMany annotation in the Article entity should be used on a non-existent database field. In other words, property $id should not be an actual field in the database table of the entity.