通过 Firestore 中类型为“reference"的字段进行查询

问题描述

我有一个名为类别"的集合，其中包含一个 ID 为 5gF5FqRPvdroRF8isOwd 的文档.

I have a collection called 'categories' containing a single document with ID: 5gF5FqRPvdroRF8isOwd.

我还有一个名为tickets"的集合.每张票都有一个参考字段，用于将票分配给特定类别.

I have another collection called 'tickets'. Each ticket has a reference field which assigns the ticket to a particular category.

门票集合中的字段称为类别"，字段类型为reference.

The field in the tickets collection is called 'category' and has a field type of reference.

在下面的代码中，categoryDocId是我要查询的类别的文档ID.

In the code below, categoryDocId is the document ID of the category I want to query by.

const categoryDocID = `5gF5FqRPvdroRF8isOwd`;

const files = await firebase
  .firestore()
  .collection('tickets')
  .where('category', '==', categoryDocID)
  .get();

为什么 files.length 返回 0?

为了测试，我将 category 字段类型更改为字符串，并将其设置为类别 ID 而不是直接引用.这正确返回了分配给该类别的票证，这让我相信这与我如何查询 reference 字段有关.

For testing, I changed the category field type to string, and set it to the category ID instead of a direct reference. This correctly returned tickets assigned to the category, which leads me to believe it's something about how I'm querying a reference field.

推荐答案

如您所见 此处 在文档中，引用数据类型用于存储 文档引用.

As you will read here in the doc, the Reference Data Type is used to store DocumentReferences.

如果要在查询中使用，不能使用简单的字符串，既不能是文档的UID(即'5gF5FqRPvdroRF8isOwd')，也不能是字段中存储的字符串值(即'/categories/5gF5FqRPvdroRF8isOwd').

If you want to use it in a query, you cannot use a simple string, neither the UID of the document (i.e. '5gF5FqRPvdroRF8isOwd'), nor the string value that is stored in the field (i.e. '/categories/5gF5FqRPvdroRF8isOwd').

您必须构建一个 DocumentReference 并在您的查询中使用它，如下所示:

You have to build a DocumentReference and use it in your query, as follows:

const categoryDocRef = firebase.firestore()
   .collection('categories')
   .doc('5gF5FqRPvdroRF8isOwd');

const files = await firebase
  .firestore()
  .collection('tickets')
  .where('category', '==', categoryDocRef)
  .get();

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