Firebase -how to run a calculation using a Cloud Function

I have a food app with a star system. Every time a user selects a rating/star I send their rating to the database and then run a firebase transaction to update the total amount of users who left a rating.

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          // ...      })  }  

When displaying the actual rating I pull the the post which has the totalUsersCount as a property, I pull all of the users actual ratings, add them all together, and then feed both numbers into an algo to spit out the actual rating. I do all of this on the client. How can I do the same thing "I pull all of the users actual rating, add them all together" with a Cloud Function, that is similar to this answer?

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)       })   })  

This isn't a question about the algoToComputeStarRating, that I can do on the client. I want to add all of the user's ratings together using a Cloud Function, then just add that result as a property to the post. That way when I pull the post all I have to do is:

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)  })  

Database structure:

@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  

This is what I tried so far:

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);              });          }      });  });  

https://stackoverflow.com/questions/66010766/firebase-how-to-run-a-calculation-using-a-cloud-function February 02, 2021 at 09:32PM