在Cloud Firestore中查找具有特定参考的所有文档 [英] Finding all docs with specific reference in Cloud Firestore

问题描述

在Cloud Firestore上，我以这种方式拥有参考其他文档的文档:

On Cloud Firestore I have documents with reference to another document this way:

在我的示例中，文档Collection A/WJQ9yx67RrqHWQoEp0e2指的是文档Collection B/rFOEwdw5go4dbitOCXyC，但是当然，可能有无限多个文档指的是所提到的文档.

In my example, document Collection A/WJQ9yx67RrqHWQoEp0e2 is referring to document Collection B/rFOEwdw5go4dbitOCXyC, but there of course, could be infinitely docs referring to one mentioned.

现在，我想找出Collection A的所有文档，这些文档都引用了非常具体的文档Collection B/rFOEwdw5go4dbitOCXyC.

Now I would like to find out all the docs of Collection A which are referring to this very specific document Collection B/rFOEwdw5go4dbitOCXyC.

这怎么可能?我该如何实现?

与此有关的Firebase文档尚不清楚.

Documentation of Firebase is bit unclear with this.

推荐答案

很对，不幸的是，在文档中没有实际使用Reference数据类型的示例，实际上唯一提及的是在受支持的数据类型部分.

You're right, there's unfortunately no example of actually making use of a Reference data type in the documentation, in fact the only a mention of it is in the Supported Data Types section.

尽管最终，Reference可以像Firestore中可用的任何其他数据类型一样使用，因此可以用于过滤&也可以对数据进行排序.

Ultimately though, a Reference can be used just like any other data type available in Firestore, so can be used to filter & sort data too.

要实现此目标，您需要构造一个指向Collection B中文档的Reference，然后使用where子句来过滤Collection A的reference值上的数据.例如，在JavaScript中:

To achieve what you're after, you would need to construct a Reference that points to the document in Collection B and then use a where clause to filter data on the reference value of Collection A. For example in JavaScript:

// Create a reference to the specific document you want to search with
var reference = db.collection("Collection B").doc("rFOEwdw5go4dbitOCXyC");

// Construct a query that filters documents matching the reference
var query = db.collection("Collection A").where("reference", "==", reference);

查看 Firebase JavaScript SDK中isEqual()的源，通过简单地检查路径是否匹配来执行Reference(扩展为Query)的比较:

Looking at the source for isEqual() in the Firebase JavaScript SDK, comparing of a Reference (extends Query) is performed by simply checking that the paths match:

  isEqual(other: Query): boolean {
    // [...]
    const sameRepo = this.repo === other.repo;
    const samePath = this.path.equals(other.path);
    const sameQueryIdentifier =
      this.queryIdentifier() === other.queryIdentifier();

    return sameRepo && samePath && sameQueryIdentifier;
  }

这似乎很像在两者上都调用toString()并比较字符串值.

This would seem to be much like calling toString() on both and comparing the string values.

昨天我制作了一个类似示例，这使我测试了存储Reference的可能用途，以便也可以在这里申请.

I produced a similar example yesterday which lead me to test the possible uses of storing a Reference, so that may also apply here.

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