ManyToMany 新值必须是数组或 \Traversable 的实例，给定“NULL”

Question

我的 Symfony 4.2.6 应用程序中有一个 ManyToMany 关系，我希望它可以为空。

所以我的第一个实体 SpecialOffers 如下：

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

/**
 * @ORM\Entity(repositoryClass="App\Repository\SpecialOfferRepository")
 */
class SpecialOffer
{
    /**
     * @ORM\ManyToMany(targetEntity="App\Entity\Neighbourhood", inversedBy="specialOffers")
     */
     private $neighbourhood;

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

    /**
     * @return Collection|Neighbourhood[]
     */
    public function getNeighbourhood(): Collection
    {
        return $this->neighbourhood;
    }

    public function addNeighbourhood(Neighbourhood $neighbourhood): self
    {
        if (!$this->neighbourhood->contains($neighbourhood)) {
            $this->neighbourhood[] = $neighbourhood;
        }

        return $this;
    }

    public function removeNeighbourhood(Neighbourhood $neighbourhood): self
    {
        if ($this->neighbourhood->contains($neighbourhood)) {
            $this->neighbourhood->removeElement($neighbourhood);
       }

       return $this;
   }
}

它与邻里类别有关：

/**
 * @ORM\Entity(repositoryClass="App\Repository\NeighbourhoodRepository")
 */
class Neighbourhood implements ResourceInterface
{
    /**
     * @ORM\ManyToMany(targetEntity="App\Entity\SpecialOffer", mappedBy="neighbourhood")
     */
    private $specialOffers;

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

        /**
     * @return Collection|SpecialOffer[]
     */
    public function getSpecialOffers(): Collection
    {
        return $this->specialOffers;
    }

    public function addSpecialOffer(SpecialOffer $specialOffer): self
    {
        if (!$this->specialOffers->contains($specialOffer)) {
            $this->specialOffers[] = $specialOffer;
            $specialOffer->addNeighbourhood($this);
        }

        return $this;
    }

    public function removeSpecialOffer(SpecialOffer $specialOffer): self
    {
         if ($this->specialOffers->contains($specialOffer)) {
            $this->specialOffers->removeElement($specialOffer);
            $specialOffer->removeNeighbourhood($this);
        }

        return $this;
    }
}

最后的形式是

class SpecialOfferType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add(
                'neighbourhood',
                EntityType::class,
                [
                    'class' => Neighbourhood::class,
                    'label' => 'form.neighbourhood.label',
                    'translation_domain' => 'Default',
                    'required' => false,
                    'placeholder' => 'form.neighbourhood.all'
                ]
             );
        }
   }

但是，当我没有在表单中选择特别优惠的特定社区时，我会收到以下错误： Could not determine access type for property "neighbourhood" in class "App\Entity\SpecialOffer": The property "neighbourhood" in class "App\Entity\SpecialOffer" can be defined with the methods "addNeighbourhood()", "removeNeighbourhood()" but the new value must be an array or an instance of \Traversable, "NULL" given.

无论如何，我可以让我的特别优惠包含社区数组或仅包含 null 吗？

我觉得我忽略了一些非常明显的事情，任何帮助将不胜感激

Answer 1

测试=>

$builder
            ->add(
                'neighbourhood',
                EntityType::class,
                [
                    'class' => Neighbourhood::class,
                    'label' => 'form.neighbourhood.label',
                    'translation_domain' => 'Default',
                    'required' => false,
                    'multiple' => true,
                    'placeholder' => 'form.neighbourhood.all'
                ]
             );