Symfony 6
教义3

Titelmeta实体类

<?php

namespace App\Entity;

use Doctrine\DBAL\Types\Types;
use Doctrine\ORM\Mapping as ORM;
use DateTime;

/**
 * Titelmeta
 *
  
  …

 * @ORM\Entity
 */
class Titelmeta
{
    …
    
    /**
     * @var \Isbn
     *
     * @ORM\Column(name="ISBN_mobi", type="bigint", nullable=false, options={"unsigned"=true})
     * @ORM\ManyToOne(targetEntity="Isbn")
     * @ORM\JoinColumns({
     *   @ORM\JoinColumn(name="ISBN_mobi", referencedColumnName="isbn")
     * })
     */
    private $isbnMobi;

    …

    public function getIsbnMobi(): ?Isbn
    {
        return $this->isbnMobi;
    }

}

Isbn实体类

<?php

namespace App\Entity;

use Doctrine\DBAL\Types\Types;
use Doctrine\ORM\Mapping as ORM;

/**
 * Isbn
 *
 * @ORM\Table(name="isbn", uniqueConstraints={@ORM\UniqueConstraint(name="isbn", columns={"isbn"})})
 * @ORM\Entity
 */
class Isbn
{
    /**
     * @var int
     *
     * @ORM\Column(name="isbn", type="bigint", nullable=false, options={"unsigned"=true})
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="IDENTITY")
     */
    private $isbn;

    …

    public function __toString()
    {
        return (string) $this->getIsbn();
    }

    public function getIsbn(): ?string
    {
        return $this->isbn;
    }

    …

}

我有一个名为$record的结果对象
return（$count）;
App\Entity\Titelmeta {#901 ▼
-isbnMobi：“97812345678”
}
public void println（）;
App\Entity\Titelmeta：：getIsbnMobi（）：返回值必须是类型？App\Entity\Isbn，返回字符串

我不明白有人能帮帮忙吗。