javascript - 从 Firestore 获取记录进行分页 - Ionic/Angular

Question

我正在尝试按照文档从 Firestore 中获取前 25 条记录，如下所示。

注意:我的要求是获取我尝试使用 current25 = documentSnapshots.docs; 的前 25 条 记录，它不会返回 25 条记录的数组.

var first = db.collection("cities")
        .orderBy("population")
        .limit(25);

return first.get().then(function (documentSnapshots) {

// *** I am stuck here as I am not getting the array ***
var current25 = documentSnapshots.docs;
  console.log(current25);
  // 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);
});

Answer 1

您无法返回 promise ，因为您没有给予足够的时间来解决 promise 。为了解决您的问题，您必须使您的函数异步并等待 promise 获取文档。

async function yourfunction(...){

   var first = db.collection("cities")
        .orderBy("population")
        .limit(25);

   const documentSnapshots = await first.get();


   var current25 = documentSnapshots.docs;
   console.log(current25);
   // 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);

   return "What you want to return";
}