我已经在我的系统中实现了类似的功能，我使用了Firebase Cloud Functions
你可以这样做：
每当get被添加到数据库的特定位置时，将'likesCounter'递增1：

exports.countLikes = functions.firestore
.document('likes').onWrite((change, context) => {
 const data = change.after.val();
 const count = Object.keys(data).length;
 return change.after.document.collection('likesCount').set(count - 1);
});

^^您可以将这些代码放在firebase函数项目文件夹的index.js文件中。
你需要修改上面的代码来适应你的数据库的数据结构，如果你不熟悉的话，请按照steps来开始你的firebase项目的云函数。

• • 2023年更新**

正如Runaud所说，使用admin.firestore.FieldValue.increment()效率更高，成本更低。

exports.countLikes = firebase.firestore.document('likes').onWrite((change, context) => {
    return admin
         .firestore()
         .collection("users")
         .doc(context.userID)
         .update({
            likesCount: admin.firestore.FieldValue.increment(1),
          });
}

我已经通过onCreate()方法达到了要求
代码如下：

const functions = require('firebase-functions');
const admin = require('firebase-admin');

admin.initializeApp();
const db = admin.firestore();

exports.getLikeCount = functions.firestore
    .document('likes/{likeId}')
    .onCreate((snap, context) => {
        // Get an object representing the document (get created like data)
        const likeData = snap.data();

        // Get feed_id from created like data
        const feedId = likeData['feed_id'];

        // Create feed ref from feed_id which get from created like data
        const feedRef = db.collection('feeds').doc(feedId);

        return feedRef
            .get()
            .then(doc => {
                // Get current likesCount for feed
                const likesCount = doc.data().likesCount;

                // Increase likesCount with +1 for get feed
                return feedRef.update({likesCount: likesCount + 1});
            })

    });