响应的异步Firebase查询 [英] Asynchronous Firebase query to response
问题描述
我正在尝试从firebase集合中获取所有文档，创建一个列表，并根据需要使用Cloud Function返回它，但是我在JavaScript的异步特性方面苦苦挣扎.到目前为止，这是我的代码:
I'm trying to get all documents from a firebase collection, create a list and return it on request with a Cloud Function, but I'm struggling with the asynchronous nature of JavaScript. Here's my code so far:
firebase.initializeApp(firebaseConfig);
const db = firebase.firestore();
const items = "";
async function buildItems() {
db.collection("reminders").get().then((QuerySnapshot) => {
QuerySnapshot.forEach((item) => {
items.concat("<li>" + item.data().name + "</li>");
console.log(items);
});
})
}
exports.view = functions.https.onRequest((req, res) => {
buildItems().then(
res.status(200).send(`<!doctype html>
<head>
<title>Reminders</title>
</head>
<body>
<ul>
${items}
</ul>
</body>
</html>`))});
包括我尝试过的基于承诺的代码(这是错误的，我不知道如何解决)
firebase.initializeApp(firebaseConfig);
const db = firebase.firestore();
function buildItems() {
return new Promise((resolve) => {
resolve(db.collection("reminders").get())
});
}
exports.view = functions.https.onRequest((req, res) => {
buildItems(reminders => {
let items = "";
reminders.then((qs) => {
qs.forEach(items.concat("<li>" + qs.data().name + "</li>"))
}).then(resolve(items));
}).then( items =>
res.status(200).send(`
<!doctype html>
<head>
<title>Reminders</title>
</head>
<body>
<ul>
${items}
</ul>
</body>
</html>`))});
输出始终是相同的:绝对没有任何内容显示在浏览器或控制台上.我已经尝试过此代码的变体，但到目前为止没有成功.
The output is always the same: absolutely nothing is displayed on the browser or to the console. I've tried variations of this code, but no success so far.
提前谢谢！
推荐答案
我稍微清理了一下代码，并用async await替换了基于Promise的代码.您可以尝试运行此代码:
I cleaned the code up a bit and replaced your Promise based code with async await. You can try running this:
异步等待版本
firebase.initializeApp(firebaseConfig);
const db = firebase.firestore();
const buildItems = async () => {
return db.collection('reminders').get();
};
exports.view = functions.https.onRequest(async (req, res) => {
try {
const reminders = await buildItems();
let items = '';
reminders.forEach(qs => {
items.concat(`<li> ${qs.data().name} </li>`);
});
return res
.status(200)
.send(`
<!doctype html>
<head>
<title>Reminders</title>
</head>
<body>
<ul>
${items}
</ul>
</body>
</html>
`);
} catch (error) {
/** Handle error here */
}
});
基于承诺的版本
firebase.initializeApp(firebaseConfig);
const db = firebase.firestore();
const buildItems = () => {
return db.collection('reminders').get();
};
exports.view = functions.https.onRequest((req, res) => {
buildItems()
.then(reminders => {
let items = '';
reminders.forEach(qs => {
items.concat(`<li> ${qs.data().name} </li>`);
});
return res
.status(200)
.send(`
<!doctype html>
<head>
<title>Reminders</title>
</head>
<body>
<ul>
${items}
</ul>
</body>
</html>
`);
})
.catch(error => {
/** Handle Error here */
});
});
如果仍然遇到问题，则应尝试检查集合reminders中是否确实包含要获取的文档.
If you are having still having trouble, you should try if the collection reminders actually contains the documents you want to fetch.
.size属性在Firebase查询快照结果的[QuerySnapShots][1]中可用.如果快照大小为0.
The .size property is available in [QuerySnapShots][1] in Firebase query snapshot results. If the snapshot size is 0.
这篇关于响应的异步Firebase查询的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
