问题描述

我正在使用 嵌入 Symfony 表单来添加和删除Tag 实体直接来自文章编辑器.文章 是拥有方 关联:

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，因为它始终为真，如果不是，则根本不会将新标签持久化到数据库中.这是 Tag 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;
    }
}

我已将 $name 设置为唯一的，因为我想每次在表单中输入相同的名称时都使用相同的标签.但它不能这样工作，我得到了例外:

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:

违反完整性约束:1062 重复条目

Integrity constraint violation: 1062 Duplicate entry

我需要更改什么才能使用 article_tag，这是提交标签名称时的默认连接表，它已经在 Tag 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

我几个月来一直在与类似的问题作斗争，终于找到了一个似乎在我的应用程序中运行良好的解决方案.这是一个复杂的应用程序，有很多多对多关联，我需要以最高效率处理它们.

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.

解决方案部分解释如下: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

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

您的代码已经完成了一半:

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;
}

基本上我添加的内容是在关系的拥有方设置 indexedBy="name" 和 fetch="EXTRA_LAZY"，这在您的案例是文章实体(您可能需要水平滚动代码块才能看到添加内容):

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;

您可以阅读在这里了解 fetch="EXTRA_LAZY" 选项.

你可以在此处阅读 indexBy="name" 选项.

接下来，我将您的 addTag() 方法的版本修改如下:

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:??空合并运算符需要 PHP7+.

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

通过将标签的获取策略设置为EXTRA_LAZY，以下语句会导致 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，请参阅上面的相关 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: 只有在设置了传递给它的实体的PRIMARY KEY 字段时，它才能返回true.当使用像 ArrayCollection::contains() 这样的方法时，Doctrine 只能根据该实体的 PRIMARY KEY 查询数据库/实体映射中的现有实体.如果 Tag 实体的 name 属性只是一个 UNIQUE KEY，这可能就是它总是返回 false 的原因.您需要一个PRIMARY KEY才能有效地使用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.

addTag() 方法中 if 块之后的其余代码通过 PRIMARY KEY 属性中的值(首选，如果不为空)或通过 Tag 实体的散列(在 Google 中搜索PHP + spl_object_hash"，Doctrine 用于索引实体).因此，您正在创建一个索引关联，以便如果您在刷新前两次添加相同的实体，它只会在相同的键处重新添加，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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