学说多对多的自我引用和互惠 [英] Doctrine's Many-To-Many Self-Referencing and reciprocity
问题描述
默认情况下，自我引用 ManytoMany 关系在Doctrine下涉及一个拥有方和一个反面，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的互惠关系？
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 \Doctrine\Common\Collections\ArrayCollection();
}
// ...
}
所以，将 entity1 添加到 entity2 s 朋友 entity2 将在 entity1 的朋友中。
So, adding entity1 to entity2s friends implies that entity2 will be in entity1s friends.
推荐答案
有很多方法可以解决这个问题，这一切都取决于朋友关系的要求。
There are a number of ways to solve this problem, all depending on what the requirements for the "friends" relation are.
单向
一个简单的方法是使用单向ManyToMany关联，并将其视为双向的关联（保持双方在同步）：
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 \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);
}
}
// ...
}
当您调用 $ userA-> addFriend（$ userB）， $ userB 将被添加到 $ userA 中的friends-collection中，而 $ userA 将被添加到朋友中收集 $ userB 。
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.
它还会导致2条记录添加到friends表（1 ，2和2,1）。虽然这可以看作是重复的数据，但它会简化你的代码。例如，当您需要查找 $ userA 的所有朋友时，您可以简单地：
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:
SELECT u FROM User u JOIN u.friends f WHERE f.id = :userId
不需要检查2个不同的属性，就像双向关联一样。
No need to check 2 different properties as you would with a bidirectional association.
双向
当使用双向关联时， User entity将具有2个属性， $ myFriends 和 $ friendsWithMe 例如。您可以按照上述方式使其保持同步。
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.
主要区别在于，在数据库级别上，只有一个记录代表关系（1 ，2或2,1）。这使得查找所有朋友的查询更复杂一些，因为您必须检查这两个属性。
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.
您当然可以在数据库中使用2条记录确定 addFriend（）将更新 $ myFriends 和 $ friendsWithMe （并保持对方同步）。这将增加您的实体的一些复杂性，但查询变得不那么复杂。
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.
OneToMany / ManyToOne
如果您需要一个用户可以添加朋友的系统，但该朋友必须确认他们确实是朋友，则需要将该确认存储在连接表中。然后你不再有一个ManyToMany关联，但是像用户< - OneToMany - > 友谊< - ManyToOne - > 用户。
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.
您可以阅读我关于这个主题的博文：
You can read my blog-posts on this subject:
- Doctrine 2: How to handle join tables with extra columns
- More on one-to-many/many-to-one associations in Doctrine 2
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