Firebase - 如何使用云函数运行计算

Question

我有一个带有星级系统的美食应用。每次用户选择评分/星级时，我都会将他们的评分发送到数据库，然后运行 ​​firebase transaction 来更新留下评分的用户总数。

let theirRating: Double = // whatEverStarRatingTheySelected
let dict = [currentUserId: theirRating]

let reviewsRef = Database.database().reference().child("reviews").child(postId)
reviewsRef.updateChildValues(dict) { (error, ref) in

    let postsRef = Database.database().reference().child("posts").child(postId).child("totalUsersCount")
    postsRef.runTransactionBlock({ (mutableData: MutableData) -> TransactionResult in
        // ...
    })
}

在显示实际评分时，我拉出具有 totalUsersCount 作为属性的帖子，我提取所有用户的实际评分，将它们加在一起，然后将两个数字输入算法以吐出实际评分。我在客户端上完成所有这些。我怎样才能使用类似于this answer 的云函数来执行相同的操作“我将所有用户的实际评分，将它们加在一起”？

Database.database().reference().child("posts").child(postId).observeSingleEvent(of: .value, with: { (snapshot) in
 
     guard let dict = snapshot.value as? [String:Any] else { return }

     let post = Post(dict: dict)
 
     let totalUsers = post.totalUsersCount

     Database.database().reference().child("reviews").child(postId).observeSingleEvent(of: .value, with: { (snapshot) in
      
          var ratingSum = 0.0
      
          // *** how can I do this part using a Cloud Function so that way I can just read this number as a property on the post instead of doing all of this on the client ***
          for review in (snapshot.children.allObjects as! [DataSnapshot]) {
              guard let rating = review.value as? Double else { continue }
              ratingSum += rating
          }
      
          let starRatingToDisplay = self.algoToComputeStarRating(totalUsersCount: totalUsersCount, ratingsSum: ratingSum)
     })
 })

这不是关于 algoToComputeStarRating 的问题，我可以在客户端上进行。我想使用云函数将所有用户的评分加在一起，然后将该结果作为属性添加到帖子中。这样，当我拉出帖子时，我所要做的就是：

Database.database().reference().child("posts").child(postId).observeSingleEvent(of: .value, with: { (snapshot) in

    guard let dict = snapshot.value as? [String:Any] else { return }

    let post = Post(dict: dict)
         
    let totalUsersCount = post.totalUsersCount
    let ratingsSum = post.ratingsSum
    
    let starRatingToDisplay = self.algoToComputeStarRating(totalUsersCount: totalUsersCount, ratingsSum: ratingSum)
})

数据库结构：

@posts
   @postId
      -postId: "..."
      -userId: "..."
      -totalUsersCount: 22
      -ratingsSum: 75 // this should be the result from the cloud function

@reviews
    @postId
       -uid_1: theirRating
       -uid_2: theirRating
       // ...
       -uid_22: theirRating

这是我迄今为止尝试过的：

exports.calculateTotalRating = functions.https.onRequest((data, response) => {

    const postId = data.postId;
    
    const totalUsersCtRef = admin.database().ref('/posts/' + postId + '/' + 'totalUsersCt');
    const postsRef = admin.database().ref('/posts/' + postId);

    admin.database().ref('reviews').child(postId).once('value', snapshot => {

        if (snapshot.exists()) {

            var ratingsSum = 0.0;

            snapshot.forEach(function(child) {

                ratingsSum += child().val()
            })
            .then(() => { 
            
                return postsRef.set({ "ratingsSum": ratingsSum})          
            })
            .then(() => { 
            
                return totalUsersCtRef.set(admin.database.ServerValue.increment(1));                
            }) 
            .catch((error) => {
                console.log('ERROR - calculateTotalRating() Failed: ', error);
            });
        }
    });
});

Answer 1

我使用这个answer：

exports.calculateTotalRating = functions.https.onRequest((data, response) => {

    const postId = data.postId;
    
    const postsRef = admin.database().ref('/posts/' + postId);
    const totalUsersCtRef = admin.database().ref('/posts/' + postId + '/' + 'totalUsersCt');

    var ratingsSum = 0.0;

    admin.database().ref('reviews').child(postId).once('value', snapshot => {

        if (snapshot.exists()) {

            snapshot.forEach((child) => {

                ratingsSum += child().val()
            })
            console.log('ratingsSum: ', ratingsSum);

            return postsRef.update({ "ratingsSum": ratingsSum }).then(() => { 
                return totalUsersCtRef.set(admin.database.ServerValue.increment(1));                
            })
            .catch((error) => {
                console.log('ERROR - calculateTotalRating() Failed: ', error);
            });   
        }
    });
});

Answer 2

我认为这应该为您提供一个良好的开端。我使用了触发器，因此所有更新都会自动发生，您的快速听众将立即获得新的评级。 :) 虽然我不确定您的 let post = Post(dict: dict) 将如何解析 [String: Any] 字典。

//We are adding a event listner that will be triggered when any child under the reviews key is modified. Since the key for updated review can be anything we use wildcards `{autoId}`.
exports.calculateTotalRating = functions.database
  .ref("reviews/{autoId}")
  .onUpdate((snapshot, context) => {


    if (snapshot.exists()) { //For safety check that the snapshot has a value
      const ratingsDict = snapshot.val(); //The updated reviews object you set using `reviewsRef.updateChildValues(dict)`

      const autoId = context.params.autoId; //Getting the wildcard postId so we can use it later 

      //Added due to error in understanding the structure of review object. Can be ignored. 
      //delete ratingsDict("totalUserCount");
      //delete ratingsDict("ratingsSum");

      const totalUsers = Object.keys(ratingsDict).length; //Counting how many reviews are there in the ratingsDict 

      //Sum over all the values in ratingsDict. This approach is supposedly slower, but was oneliner so used it. Feel free to modify this with a more efficient way to sum values once you are more comfortable with cloud functions.
      const ratingsSum = Object.keys(ratingsDict).reduce(
        (sum, key) => sum + parseFloat(ratingsDict[key] || 0),
        0
      );  

      //Saving the computed properties.
      ratingsDict["totalUserCount"] = totalUsers;
      ratingsDict["ratingsSum"] = ratingsSum;

      //Updating posts with new reviews and calculated properties
      return functions.database.ref("posts").child(autoId).set(ratingsDict);
    }
  });

我觉得你是新手，所以你可以按照这个指南to create cloud functions。在您应用的顶级目录中，只需运行firebase init functions 并从Use an existing project 中选择您的项目。这应该为您创建一个带有 index.js 文件的函数文件夹，您可以在其中添加此代码。然后运行firebase deploy --only functions:calculateTotalRating。