如何在 Firestore 中处理多个相关的异步查询
我想构建一个以 Firebase 作为后端的问答应用。Firestore 中有三个集合questions：answers和repliesToAnswers。中的文档question有 1 个字段content，中的文档answers有 2 个字段answerid和content，中的文档repliesToAnswers有 3 个字段answerId，questionId并且content。
questions: {
content
}
answers: {
questionId
content
}
repliesToAnswers {
content
answerId
questionId
}
我的目标是构建一个/question/:questionId获取这样的结构化数据的 Restful API 端点
{
"content": "How to ...",
"answers": [
{
"content":"...",
"replies": [
{
"content":"..."
},
{
"content":"..."
}
]
},
{
"content":"...",
"replies":[]
}
],
}
所以我尝试编写容易出错的嵌套 Promises。
exports.getQuestion = (request, response) => {
console.log(request.params);
let questionId = request.params.questionId;
let question = {};
firebase
.firestore()
.collection('questions')
.doc(questionId)
.get()
.then(doc => {
if(!doc.exists) {
throw Error("doc not exists")
}
return doc;
})
.then(doc => {
question.username = doc.data().username
return doc.id
})
.then(id => {
// retrive answsers
let answers = [];
firebase.firestore()
.collection('answers')
.where('questionId', '==', id)
.get()
.then(snapshot => {
if (snapshot.empty) {
console.log('no answers');
return answers;
}
snapshot.forEach(ans => {
// retrive replies
let replies = [];
firebase.firestore()
.collection('repliesToAnswers')
.where('questionId','==',questionId)
.where('answerId','==', ans.id)
.get()
.then(snapshot => {
if(snapshot.empty) {
console.log(`no reply to answer(id:${ans.id}) of question(${questionId})`);
return [];
}
问题是该函数为每个答案返回了空的回复数组。它跳过了检索每个答案的回复的请求。任何人都可以帮助我吗？还是有更好的风格来实现它？
慕慕森1回答
-
Smart猫小萌
我终于Promise.all()用更优雅的代码解决了这个问题。exports.getQuestion = (request, response) => { let questionId = request.params.questionId; // let question = {}; //let answers = []; // get info except answers // { content:XXX, answers: [] } let fetchQuestion = firebase.firestore() .doc(`questions/${questionId}`) .get() .then(doc => { if(!doc.exists) { throw Error('doc not exists'); } return doc }) .then(doc => { return { content: doc.data().content, id: doc.id, answers: [] } }) .catch(error => { console.log(error) }); // return answers let fetchAnswers = firebase.firestore() .collection('answers') .where('questionId','==',questionId) .get() .then(snapshot => { if(snapshot.empty) { console.log('no replies'); return []; } else { let answers = []; snapshot.forEach(ans => { // add answers to question answers.push({ content: ans.data().content, replies: [], id: ans.id }) }) return answers; } }).catch(error => { console.log(error); }); let fetchAnsReplies = fetchAnswers.then(answers => { var promises = []; answers.forEach(ans => { var promise = firebase.firestore() .collection('repliesToAnswers') .where('answerId','==',ans.id) .get() .then(snapshot => { if(snapshot.empty) { console.log('no reply'); return; } else { snapshot.forEach(reply => { ans.replies.push({ content: reply.data() }) }) } }).catch(error => { console.log(error); }) promises.push(promise); }) return Promise.all(promises).then(() => { return answers; }) }).catch(error => { console.log(error); }) return Promise.all([fetchQuestion,fetchAnswers, fetchAnsReplies]) .then(results => { return response.json({...results[0],answers:results[2]}); }).catch(error => { console.log(error); response.status(500).json({ error: error.code }) })}
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相关分类
JavaScript