根据Firebase文档，这是怎么做的：
var first = db.collection("cities")
.orderBy("population")
.limit(25);
return first.get().then(function (documentSnapshots) {
// Get the last visible document
var lastVisible = documentSnapshots.docs[documentSnapshots.docs.length-1];
console.log("last", lastVisible);
// Construct a new query starting at this document,
// get the next 25 cities.
var next = db.collection("cities")
.orderBy("population")
.startAfter(lastVisible)
.limit(25);
});
但问题是我认为没有办法使用 get 函数，甚至无法使用snapshotChanges()来获取长度，然后减去它以用作下一个 get 的参考。任何提示将不胜感激！
更新：
我尝试手动输入索引，但无济于事，因为它返回了一个没有数据的数组。
getNewsCollectionNext() {
this.newsCollectionRef = this.afDB.collection('news', ref =>
ref.where('news_is_deleted', '==', false).orderBy('news_timestamp_post_created', 'desc')
.startAfter(1));
this.newsCollection = this.newsCollectionRef.snapshotChanges().pipe(
map(actions => actions.map(a => {
const data = a.payload.doc.data() as News;
const id = a.payload.doc.id;
return { id, ...data };
}))
);
return this.newsCollection;
}
虽然这个返回 3 个项目
getNewsCollection() {
this.newsCollectionRef = this.afDB.collection('news', ref =>
ref.where('news_is_deleted', '==', false).orderBy('news_timestamp_post_created', 'desc'));
this.newsCollection = this.newsCollectionRef.snapshotChanges().pipe(
map(actions => actions.map(a => {
const data = a.payload.doc.data() as News;
const id = a.payload.doc.id;
return { id, ...data };
}))
);
return this.newsCollection;
// console.log(this.newsList);
}
更新2：我使"下一个"功能起作用！
tl;dr：所以我所做的就是解开文档的包装。 有效负载并将我的可观察类型更改为任何以防止冲突:) 所以这是我在服务中的代码
getNewsCollection() {
this.newsCollectionSubscription = this.newsService.getNewsCollection().
subscribe(newsCollection => {
this.newsCollection = newsCollection;
console.log('t2est',newsCollection[newsCollection.length - 1].doc);
if(newsCollection){
this.snapshot = newsCollection[newsCollection.length - 1].doc;
}
});
}
getNextNewsCollection() {
this.newsCollectionSubscription = this.newsService.getNextNewsCollection(this.snapshot).
subscribe(newsCollection => {
this.newsCollection = newsCollection;
// console.log('t2est',newsCollection[1].doc);
console.log(newsCollection);
});
}
在我的新闻卡上
getNewsCollection() {
this.newsCollectionSubscription = this.newsService.getNewsCollection().
subscribe(newsCollection => {
this.newsCollection = newsCollection;
console.log('t2est',newsCollection[newsCollection.length - 1].doc);
if(newsCollection){
this.snapshot = newsCollection[newsCollection.length - 1].doc;
}
});
}
getNextNewsCollection() {
this.newsCollectionSubscription = this.newsService.getNextNewsCollection(this.snapshot).
subscribe(newsCollection => {
this.newsCollection = newsCollection;
// console.log('t2est',newsCollection[1].doc);
console.log(newsCollection);
});
}
请看下面的HTML页面，该页面显示了(纯Javascript(如何修改query以便逐页显示文档。
您可以将其下载到本地文件夹/目录，调整配置对象并使用浏览器打开它。单击该按钮将在控制台中显示文档 3 x 3。
请注意，在此简单 POC 中，当分页到达集合末尾时，没有错误处理。
<html>
<head>
<script src="https://www.gstatic.com/firebasejs/5.5.3/firebase-app.js"></script>
<script src="https://www.gstatic.com/firebasejs/5.5.3/firebase-firestore.js"></script>
</head>
<body>
<button id="myBtn">Display next subset</button>
<script>
document.getElementById("myBtn").addEventListener("click", function () {
displayNextPaginationSubset();
});
// Initialize Firebase
var config = {
apiKey: "....",
authDomain: "....",
databaseURL: "....",
projectId: "...."
};
firebase.initializeApp(config);
var db = firebase.firestore();
var query = db.collection("cities")
.orderBy("population")
.limit(3);
function displayNextPaginationSubset() {
query.get().then(function (documentSnapshots) {
documentSnapshots.forEach(function(doc) {
// doc.data() is never undefined for query doc snapshots
console.log(doc.id, " => ", doc.data());
});
// Get the last visible document
var lastVisible = documentSnapshots.docs[documentSnapshots.docs.length-1];
console.log("last", lastVisible);
// Construct a new query starting at this document,
// get the next 3 cities.
query = db.collection("cities")
.orderBy("population")
.startAfter(lastVisible)
.limit(3);
});
}
</script>
</body>
</html>