计算值匹配的位置，并检索计数和值Firebase和Vue

Question

我有一个很大的注册列表，我希望在前5个较少且最常用的列表中显示：

我不知道Firebase Cloud Firestore对此类操作的查询是什么样的。要从主题中的集合中检索数据，我使用：

getUserRegistrations() {
  var user = firebase.auth().currentUser;
  var userUID = user.uid;
  db
    .collection("registrations")
    .orderBy("date", "desc")
    .where("uid", "==", userUID)
    .get()
    .then(querySnapshot => {
      const userRegistrations = [];
      querySnapshot.forEach(doc => {
        const data = {
          registration_id: doc.id,
          experience_id: doc.data().experience_id,
          uid: doc.data().uid,
          title: doc.data().title,
          date: doc.data().date
        };
        userRegistrations.push(data);
      });
      this.userRegistrations = userRegistrations;
    });
},

Answer 1

您可以使用limit()功能仅列出5个文档：

db
    .collection("registrations")
    .where("uid", "==", userUID)
    .orderBy("date", "desc")
    .limit(5)
    .get()
    .then(querySnapshot => {
      const userRegistrations = [];
      querySnapshot.forEach(doc => {
        const data = {
          registration_id: doc.id,
          experience_id: doc.data().experience_id,
          uid: doc.data().uid,
          title: doc.data().title,
          date: doc.data().date
        };
        userRegistrations.push(data);
      });
      this.userRegistrations = userRegistrations;
    });