ManyToMany新值必须是\ Traversable的数组或实例，给出“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null。

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'
                ]
             );
        }
   }

但是当我没有在我的表格中为特价商品选择特定的社区时，我收到以下错误：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.

无论如何我可以做到这一点，以便我的特别优惠包含和一系列的邻居或只是null？

我觉得我忽略了一些非常明显的东西，任何帮助都会非常感激

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'
                ]
             );

Answer 2

由于你的实体上的字段都是多对多的，因此期望一个数组（或类似的），并且表单字段是EntityType，它将返回一个预期类型的​​实体或null，我觉得有某种形式的不对称。

我会考虑从一开始就使用CollectionType或者至少将表单上的multiple选项设置为true，以便返回值是一个数组。

另一种选择是将DataTransformer添加到表单字段，该表字段将null转换为空数组，将一个实体转换为一个实体的数组，反之亦然。