如何基于Promise的动态响应构建Firestore查询链 [英] How to build a Firestore query chain based on a dynamic response from a promise

问题描述

比方说，我需要针对我在诺言中收到的一系列主题来查询Firestore:

Let's say I need to query Firestore against a collection of subjects that I receive in a promise:

const subjects: string[] = await getSubjects(); //response: ['Math', 'Science', 'History'];

由于我不知道在任何给定时间承诺中会返回多少主题，我将如何动态生成下面的链，以便正确查询Firestore?

Since I don't know how many subjects might be returned in the promise at any given time, how would I go about dynamically generating the chain below so I can properly query Firestore?

ref.where('subject[subjects[0].toLowerCase()]', '==' , true)
    .where('subject[subjects[1].toLowerCase()]', '==' , true)
    .where('subject[subjects[2].toLowerCase()]', '==' , true);

返回的主题越多，需要生成的 .where()方法就越多.

The more subjects that are returned, the more .where() methods it would need to generate.

推荐答案

创建查询遵循一个构建器模式:当您调用 where 时，它会返回一个 Query ，然后在该查询上查询，您可以再次调用 where .

Creating a Query follows a builder pattern: when you call where it returns a Query and on that Query you can call where again.

因此，如果您有一个主题数组并且想要创建一个主题查询，则可以执行以下操作:

So if you have an array of subjects and want to create a query of those, you can do:

var query = firebase.firestore().collection("bla");
['Math', 'Science', 'History'].forEach((subject) => {
   query = query.where(`subject[${subject}.toLowerCase()]'`, '==' , true);
})
query.get()....

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请注意，如今的Firestore支持 array-contains-any 运算符，该运算符的伸缩性明显好于这些类型的运算，并且一次可以处理多达10个主题.

---

Note that Firestore nowadays supports an array-contains-any operator, which scale significantly better for these types of operations and can deal with up to 10 subjects at once.

要使用此功能，您的文档将需要包含一个数组 主题，例如:

To use this you documents will need to contain an array subjects, like:

subjects: ['Math', 'Biology']

然后使用以下命令进行查询:

And then you'd query it with:

var query = firebase.firestore().collection("bla")
  .where('subjects', 'array-contains-any', ['Math', 'Science', 'History']);
query.get()...

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