“简单”CollectionType包含错误

Question

I try to make a form for an entity called Product with an embedded form from an entity Barcode. When I try to go to the form to add one product, I have the message "Return value of App\Entity\Product::getBarcodes() must implement interface Doctrine\Common\Collections\Collection, null returned". I say in __construct to initialize the barcodes to implement the Collection but still the same..

My Barcode Entity

<?php

namespace App\Entity;

use Doctrine\ORM\Mapping as ORM;

/**
 * @ORM\Entity(repositoryClass="App\Repository\BarcodeRepository")
 */
class Barcode
{
    /**
     * @ORM\Id()
     * @ORM\GeneratedValue()
     * @ORM\Column(type="integer")
     */
    private $id;

    /**
     * @ORM\Column(type="string", length=255)
     */
    private $code;

    /**
     * @ORM\ManyToOne(targetEntity="App\Entity\Product", inversedBy="barcodes")
     * @ORM\JoinColumn(nullable=false)
     */
    private $product;

    public function __construct(Product $product = null)
    {
        $this->product = $product;
    }

    public function getId(): ?int
    {
        return $this->id;
    }

    public function getCode(): ?string
    {
        return $this->code;
    }

    public function setCode(string $code): self
    {
        $this->code = $code;

        return $this;
    }

    public function getProduct(): ?Product
    {
        return $this->product;
    }

    public function setProduct(?Product $product): self
    {
        $this->product = $product;

        return $this;
    }
}

My Product Entity :

<?php

namespace App\Entity;

use Doctrine\Common\Collections\ArrayCollection;
use Doctrine\Common\Collections\Collection;
use Doctrine\ORM\Mapping as ORM;
use Symfony\Component\Validator\Constraints as Assert;
use Symfony\Bridge\Doctrine\Validator\Constraints\UniqueEntity;

/**
 * @ORM\Entity()
 * @ORM\InheritanceType("JOINED")
 * @ORM\DiscriminatorColumn(name="type", type="string")
 * @UniqueEntity("slug")
 */
class Product
{
    /**
     * @ORM\Id()
     * @ORM\GeneratedValue()
     * @ORM\Column(type="integer")
     */
    protected $id;

    /**
     * @ORM\Column(type="string", length=255)
     */
    protected $name;

    /**
     * @ORM\Column(type="string", length=255)
     * @Assert\Regex(pattern="/\.(svg|png)$/")
     */
    protected $picture;

    /**
     * @ORM\Column(type="boolean")
     */
    protected $is_activated;

    /**
     * @ORM\Column(type="string", length=255, nullable=true)
     */
    protected $comments;

    /**
     * @ORM\Column(type="datetime")
     */
    protected $created_at;

    /**
     * @ORM\OneToMany(targetEntity="App\Entity\Barcode", mappedBy="product", orphanRemoval=true, cascade={"all"})
     */
    protected $barcodes;

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

    public function getId(): ?int
    {
        return $this->id;
    }

    public function getName(): ?string
    {
        return $this->name;
    }

    public function setName(string $name): self
    {
        $this->name = $name;

        return $this;
    }

    public function getPicture(): ?string
    {
        return $this->picture;
    }

    public function setPicture(string $picture): self
    {
        $this->picture = $picture;

        return $this;
    }

    public function getIsActivated(): ?bool
    {
        return $this->is_activated;
    }

    public function setIsActivated(bool $is_activated): self
    {
        $this->is_activated = $is_activated;

        return $this;
    }

    public function getComments(): ?string
    {
        return $this->comments;
    }

    public function setComments(?string $comments): self
    {
        $this->comments = $comments;

        return $this;
    }

    public function getCreatedAt(): ?\DateTimeInterface
    {
        return $this->created_at;
    }

    public function setCreatedAt(\DateTimeInterface $created_at): self
    {
        $this->created_at = $created_at;

        return $this;
    }

    /**
     * @return Collection|Barcode[]
     */
    public function getBarcodes(): Collection
    {
        return $this->barcodes;
    }

    public function addBarcode(Barcode $barcode): self
    {
        if (!$this->barcodes->contains($barcode)) {
            $this->barcodes[] = $barcode;
            $barcode->setProduct($this);
        }

        return $this;
    }

    public function removeBarcode(Barcode $barcode): self
    {
        if ($this->barcodes->contains($barcode)) {
            $this->barcodes->removeElement($barcode);
            // set the owning side to null (unless already changed)
            if ($barcode->getProduct() === $this) {
                $barcode->setProduct(null);
            }
        }

        return $this;
    }

}

and my ProductType:

public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('name')
            ->add('slug')
            ->add('picture')
            ->add('barcodes', CollectionType::class, [
                'entry_type' => BarcodeType::class,
                'allow_add' => true,
                'allow_delete' => true,
                'prototype' => true,
                'by_reference' => false
            ])
            ->add('is_activated')
            ->add('comments')
        ;
    }

Answer 1

In your Product entity, allow the possibility of a null return type by changing Collection to ?Collection:

/**
 * @return Collection|Barcode[]|null
 */
public function getBarcodes(): ?Collection
{
    return $this->barcodes;
}