教义的多对多自我引用和互惠

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

默认情况下，Doctrine下的自引用ManyToMany关系涉及拥有方和反方，如文档中所述。

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

有没有办法实现双方之间没有差异的互惠协会？

Following the example in the docs:

按照文档中的示例：

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

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

    public function __construct() {
        $this->friends = new \Doctrine\Common\Collections\ArrayCollection();
    }

    // ...
}

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

因此，将entity1添加到entity2s的朋友意味着entity2将在entity1s的朋友中。

1 个解决方案

#1

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

有许多方法可以解决这个问题，所有这些都取决于对“朋友”关系的要求。

Unidirectional

单向

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):

一种简单的方法是使用单向ManyToMany关联，并将其视为双向关联（保持双方同步）：

/**
 * @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 \Doctrine\Common\Collections\ArrayCollection
     */
    private $friends;

    /**
     * Constructor.
     */
    public function __construct()
    {
        $this->friends = new \Doctrine\Common\Collections\ArrayCollection();
    }

    /**
     * @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);
        }
    }

    // ...

}

When you call $userA->addFriend($userB), $userB will be added to the friends-collection in $userA, and $userA will be added to the friends-collection in $userB.

当你拨打$ userA-> addFriend（$ userB）时，$ userB将被添加到$ userA中的friends-collection，$ userA将被添加到$ userB中的friends-collection。

It will also result in 2 records added to the "friends" table (1,2 and 2,1). While this can be seen as duplicate data, it will simplify your code a lot. For example when you need to find all friends of $userA, you can simply do:

它还会将2条记录添加到“朋友”表（1,2和2,1）中。虽然这可以看作是重复数据，但它会大大简化您的代码。例如，当您需要找到$ userA的所有朋友时，您可以简单地执行以下操作：

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

No need to check 2 different properties as you would with a bidirectional association.

无需像使用双向关联那样检查2个不同的属性。

Bidirectional

双向

When using a bidirectional association the User entity will have 2 properties, $myFriends and $friendsWithMe for example. You can keep them in sync the same way as described above.

使用双向关联时，User实体将具有2个属性，例如$ myFriends和$ friendsWithMe。您可以按照与上述相同的方式使它们保持同步。

The main difference is that on a database level you'll only have one record representing the relationship (either 1,2 or 2,1). This makes "find all friends" queries a bit more complex because you'll have to check both properties.

主要区别在于，在数据库级别上，您只有一条记录代表关系（1,2或2,1）。这使得“查找所有朋友”查询更加复杂，因为您必须检查这两个属性。

You could of course still use 2 records in the database by making sure addFriend() will update both $myFriends and $friendsWithMe (and keep the other side in sync). This will add some complexity in your entities, but queries become a little less complex.

您当然可以通过确保addFriend（）更新$ myFriends和$ friendsWithMe（并保持另一方同步）来在数据库中使用2条记录。这将在您的实体中增加一些复杂性，但查询变得不那么复杂。

OneToMany / ManyToOne

OneToMany / ManyToOne

If you need a system where a user can add a friend, but that friend has to confirm that they are indeed friends, you'll need to store that confirmation in the join-table. You then no longer have a ManyToMany association, but something like User <- OneToMany -> Friendship <- ManyToOne -> User.

如果您需要一个系统，用户可以添加朋友，但该朋友必须确认他们确实是朋友，您需要将该确认存储在连接表中。然后，您不再拥有ManyToMany关联，而是User < - OneToMany - > Friendship < - ManyToOne - > User。

You can read my blog-posts on this subject:

你可以阅读我关于这个主题的博客文章：

• Doctrine 2: How to handle join tables with extra columns
• Doctrine 2：如何处理带有额外列的连接表
• More on one-to-many/many-to-one associations in Doctrine 2
• 更多关于Doctrine 2中的一对多/多对一关联