学说的多对多自参照和互惠

问题描述

默认情况下，Doctrine 下的自引用 ManyToMany 关系涉及拥有方和反向方，如 文档.

By default, self-referencing ManyToMany relationships under Doctrine involve an owning side and an inverse side, as explained in the documentation.

有没有办法实现双方之间没有差异的互惠关联?

Is there a way to implement a reciprocal association whithout difference between both sides?

按照文档中的示例:

<?php
/** @Entity **/
class User
{
    // ...

    /**
     * @ManyToMany(targetEntity="User")
     **/
    private $friends;

    public function __construct() {
        $this->friends = new DoctrineCommonCollectionsArrayCollection();
    }

    // ...
}

因此，将 entity1 添加到 entity2 的 friends 意味着 entity2 将在 entity1的朋友.

So, adding entity1 to entity2s friends implies that entity2 will be in entity1s friends.

推荐答案

解决这个问题的方法有很多种，都取决于对朋友"关系的要求.

There are a number of ways to solve this problem, all depending on what the requirements for the "friends" relation are.

单向

一种简单的方法是使用单向多对多关联，并将其视为双向关联(保持双方同步):

A simple approach would be to use a unidirectional ManyToMany association, and treat it as if it where a bidirectional one (keeping both sides in sync):

/**
 * @Entity
 */
class User
{
    /**
     * @Id
     * @Column(type="integer")
     */
    private $id;

    /**
     * @ManyToMany(targetEntity="User")
     * @JoinTable(name="friends",
     *     joinColumns={@JoinColumn(name="user_a_id", referencedColumnName="id")},
     *     inverseJoinColumns={@JoinColumn(name="user_b_id", referencedColumnName="id")}
     * )
     * @var DoctrineCommonCollectionsArrayCollection
     */
    private $friends;

    /**
     * Constructor.
     */
    public function __construct()
    {
        $this->friends = new DoctrineCommonCollectionsArrayCollection();
    }

    /**
     * @return array
     */
    public function getFriends()
    {
        return $this->friends->toArray();
    }

    /**
     * @param  User $user
     * @return void
     */
    public function addFriend(User $user)
    {
        if (!$this->friends->contains($user)) {
            $this->friends->add($user);
            $user->addFriend($this);
        }
    }

    /**
     * @param  User $user
     * @return void
     */
    public function removeFriend(User $user)
    {
        if ($this->friends->contains($user)) {
            $this->friends->removeElement($user);
            $user->removeFriend($this);
        }
    }

    // ...

}

当你调用$userA->addFriend($userB)时，$userB会被添加到$userA，并且 $userA 将被添加到 $userB 中的朋友集合中.

SELECT u FROM User u JOIN u.friends f WHERE f.id = :userId