如何避免与Doctrine建立多重关系的重复条目？ [英] How to avoid duplicate entries in a many-to-many relationship with Doctrine?

问题描述

我正在使用嵌入Symfony表单来添加和删除标签实体直接从文章编辑器。 文章是拥有方：

I'm using an embed Symfony form to add and remove Tag entities right from the article editor. Article is the owning side on the association:

class Article
{
    /**
     * @ManyToMany(targetEntity="Tags", inversedBy="articles", cascade={"persist"})
     */
    private $tags;

    public function addTag(Tag $tags)
    {
        if (!$this->tags->contains($tags)) // It is always true.
            $this->tags[] = $tags;
    }
}

条件在这里没有帮助，因为它是总是真的，如果不是，那么根本就不会有任何新的标签将被保留到数据库。这里是标签实体：

The condition doesn't help here, as it is always true, and if it wasn't, no new tags would be persisted to the database at all. Here is the Tag entity:

class Tag
{
    /**
     * @Column(unique=true)
     */
    private $name

    /**
     * @ManyToMany(targetEntity="Articles", mappedBy="tags")
     */
    private $articles;

    public function addArticle(Article $articles)
    {
        $this->articles[] = $articles;
    }
}

我设置了 $名称为唯一，因为我每次在表单中输入相同的名称时都要使用相同的标签。但是这样做不行，我得到例外：

I've set $name to unique, because I want to use the same tag every time I enter the same name in the form. But it doesn't work this way, and I get the exception:

完整性约束违规：1062重复条目

Integrity constraint violation: 1062 Duplicate entry

需要更改以使用 article_tag ，提交标签名称时的默认连接表，这已经在标签表中？

What do I need to change to use article_tag, the default join table when submitting a tag name, that's already in the Tag table?

推荐答案

我一直在与几个月的类似问题，终于找到一个在我的应用程序中似乎很好的解决方案。这是一个复杂的应用程序，有很多对多关联，我需要以最高的效率处理它们。

I have been battling with a similar issue for months and finally found a solution that seems to be working very well in my application. It's a complex application with quite a few many-to-many associations and I need to handle them with maximum efficiency.

解决方案在这里部分解释： http://docs.doctrine-project.org/projects/doctrine-orm/en/latest/reference/faq.html#why-do-i-get-exceptions-about -unique-constraint-failures-in-em-flush

The solution is explained in part here: http://docs.doctrine-project.org/projects/doctrine-orm/en/latest/reference/faq.html#why-do-i-get-exceptions-about-unique-constraint-failures-during-em-flush

您已经在中间，您的代码：

You were already halfway there with your code:

public function addTag(Tag $tags)
{
    if (!$this->tags->contains($tags)) // It is always true.
        $this->tags[] = $tags;
}

基本上我添加的是设置 indexedBy =名称和 fetch =EXTRA_LAZY在关系的所有方面，在您的情况下文章实体（您可能需要滚动代码块水平查看添加）：

Basically what I have added to this is to set indexedBy="name" and fetch="EXTRA_LAZY" on the owning side of the relationship, which in your case is Article entity (you may need to scroll the code block horizontally to see the addition):

class Article
{
    /**
     * @ManyToMany(targetEntity="Tags", inversedBy="articles", cascade={"persist"}, indexedBy="name" fetch="EXTRA_LAZY")
     */
    private $tags;

您可以在这里阅读关于 fetch =EXTRA_LAZY选项： http：// docs。 doctrine-project.org/projects/doctrine-orm/en/latest/tutorials/extra-lazy-associations.html

You can read up about the fetch="EXTRA_LAZY" option here: http://docs.doctrine-project.org/projects/doctrine-orm/en/latest/tutorials/extra-lazy-associations.html

您可以阅读关于 indexBy =name选项通过搜索Google的Doctrine +索引关联，不用引号，并查找是Doctrine文档的一部分的结果（不能发布另一个链接，因为我的声誉不够高）

You can read up about indexBy="name" option by searching Google for "Doctrine + indexed association" without quotes, and look for the result that is part of Doctrine's docs (can't post another link because my reputation is not high enough).

接下来，我修改了您的 addTag（）方法的版本，如下所示：

Next, I modified my versions of your addTag() method as follows:

public function addTag(Tag $tags)
{
    // Check for an existing entity in the DB based on the given
    // entity's PRIMARY KEY property value
    if ($this->tags->contains($tags)) {
        return $this; // or just return;
    }

    // This prevents adding duplicates of new tags that aren't in the
    // DB already.
    $tagKey = $tag->getName() ?? $tag->getHash();
    $this->tags[$tagKey] = $tags;
}

注意 ?? null coalesce operator需要PHP7 +。

NOTE: The ?? null coalesce operator requires PHP7+.

通过将标签的提取策略设置为 EXTRA_LAZY 以下语句导致Doctrine执行SQL查询以检查数据库中是否存在具有相同名称的标签（有关更多信息，请参阅上述相关的 EXTRA_LAZY 链接）：

By setting the fetch strategy for tags to EXTRA_LAZY the following statement causes Doctrine to perform a SQL query to check if a Tag with the same name exists in the DB (see the related EXTRA_LAZY link above for more):

$this->tags->contains($tags)

注意： 只有设置了传递给该实体的实体的 PRIMARY KEY 字段时，这只能返回true。当使用像 ArrayCollection :: contains（）这样的方法时，原则只能基于该实体的PRIMARY KEY查询数据库/实体映射中的现有实体。如果标签实体的名称属性只是一个 UNIQUE KEY ，那么这可能是为什么它总是返回false。您将需要使用 PRIMARY KEY 来有效地使用 contains（）等方法。

NOTE: This can only return true if the PRIMARY KEY field of the entity passed to it is set. Doctrine can only query for existing entities in the database/entity map based on the PRIMARY KEY of that entity, when using methods like ArrayCollection::contains(). If the name property of the Tag entity is only a UNIQUE KEY, that's probably why it's always returning false. You will need a PRIMARY KEY to use methods like contains() effectively.

其余的在 addTag（）方法中的代码之后，if块将通过 PRIMARY KEY 属性中的值（首选，如果不为空）为标签的ArrayCollection创建一个键，或者通过标签实体的哈希（Google搜索PHP + spl_object_hash，由Doctrine用于索引实体）。因此，您正在创建一个索引关联，因此如果在刷新之前添加相同的实体两次，则只会在相同的键上重新添加，但不会重复。

The rest of the code in the addTag() method after the if block creates a key for the ArrayCollection of Tags either by the value in the PRIMARY KEY property (preferred if not null) or by the Tag entity's hash (search Google for "PHP + spl_object_hash", used by Doctrine to index entities). So, you are creating an indexed association, so that if you add the same entity twice before a flush, it will just be re-added at the same key, but not duplicated.

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