如何在多对多原则下插入连接 table？

Question

我正在尝试插入一个名为 post_post_category 的联结 table，它基于 Post 和 PostCategory tables [many to many], 我设法执行插入但是问题是，当我添加一个新的 post 时，它会创建一个新类别。

Post 实体：

class Post
{

...

 /**
 *  @ORM\ManyToMany(targetEntity="PostCategory", cascade={"persist"})
 *  @ORM\JoinTable(name="post_post_category",
 *      joinColumns={@ORM\JoinColumn(name="post_id", referencedColumnName="id")},
 *      inverseJoinColumns={@ORM\JoinColumn(name="post_category_id", referencedColumnName="id")}
 *   )
 */
private $categories;

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

...

public function getCategories(): ?PostCategory
{
    return $this->categories;
}

public function addCategory(PostCategory $category): self
{
    $this->categories->add($category);

    return $this;
}
}

类别实体：

class PostCategory
{
    /**
     * @ORM\Id()
     * @ORM\GeneratedValue()
     * @ORM\Column(type="integer")
     */
    private $id;

    /**
     * @ORM\Column(type="string", length=60)
     */
    private $category_description;

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

    public function getCategoryDescription(): ?string
    {
        return $this->category_description;
    }

    public function setCategoryDescription(string $category_description): self
    {
        $this->category_description = $category_description;

        return $this;
    }    
}

控制器：

...

$category->setCategoryDescription('New category');
$post->addCategory($category);

$database_manager->persist($post);
$database_manager->flush();

如何在联结点 table 中插入现有类别？

Answer 1

要将现有类别添加到 Post，您必须从数据库中检索类别

$category = $em->getRepository('AppBundle:PostCategory')->find($categoryId);
$post->addCategory($category);

如何在多对多原则下插入连接 table？

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