同步数组(针对喜欢/关注者)最佳实践 [Firebase Swift]

Synchronized Array (for likes/followers) Best Practice [Firebase Swift](同步数组(针对喜欢/关注者)最佳实践 [Firebase Swift])

问题描述

我正在尝试使用 Swift 和 Firebase 创建一个基本的跟踪算法.我目前的实现如下:

static func follow(user: FIRUser, userToFollow: FIRUser) {database.child("users").child(user.uid).observeSingleEventOfType(.Value, withBlock: { (snapshot) invar dbFollowing:NSMutableArray！= snapshot.value!["Following"] as!NSMutableArray！dbFollowing?.addObject(userToFollow.uid)self.database.child("users/"+(user.uid)+"/").updateChildValues(["Following":dbFollowing!])//以类似的方式将用户uid添加到userToFollows关注者数组}) {(错误)在print("follow - 无法检索数据 - 例外:" + error.localizedDescription)}}

这会从 Firebase 节点 Following 检索数组，添加 userToFollow 的 uid，并将新数组发布到节点 Following.这有几个问题:

1. 它是不同步的，因此如果在两个设备上同时调用它，一个数组将覆盖另一个数组，并且不会保存跟随者.
2. 如果没有追随者，它就无法处理 nil 数组，程序将崩溃(不是主要问题，我可能可以通过选项来解决).

我想知道为用户关注者或帖子点赞创建一个同步的 uid/tokens 数组的最佳做法是什么.我找到了以下链接，但似乎没有一个可以直接解决我的问题并且似乎还存在其他问题.我认为向有经验的社区询问是明智的做法，而不是把一堆解决方案一起弗兰肯斯坦.

https://firebase.googleblog.com/2014/05/handling-synchronized-arrays-with-real.htmlhttps://firebase.google.com/docs/database/ios/save-data(将数据保存为事务部分)

感谢您的帮助！

感谢 Frank，我找到了一个使用 runTransactionBlock 的解决方案.这里是:

static func follow(user: FIRUser, userToFollow: FIRUser) {self.database.child("users/"+(user.uid)+"/Following").runTransactionBlock({ (currentData: FIRMutableData!) -> FIRTransactionResult invar value = currentData?.value as?数组<字符串>如果(值 == 零){值 = [userToFollow.uid]} 别的 {如果！(值！.contains(userToFollow.uid)){价值！.append(userToFollow.uid)}}currentData.value = 值！返回 FIRTransactionResult.successWithValue(currentData)}) {(错误，提交，快照)在如果让错误=错误{print("follow - 更新后续事务 - 例外:" + error.localizedDescription)}}}

这会将 userToFollow 的 uid 添加到 user 的数组 Following 中.它可以处理 nil 值并相应地进行初始化，并且如果用户已经关注 userToFollow 的 uid，它将忽略请求.如果您有任何问题，请告诉我！

一些有用的链接:

1. firebase runTransactionBlock
的评论
2. 通过 Firebase 在 Swift 中支持/反对系统的答案
3. 我在上面发布的第二个链接

I'm trying to create a basic following algorithm using Swift and Firebase. My current implementation is the following:

static func follow(user: FIRUser, userToFollow: FIRUser) {
    database.child("users").child(user.uid).observeSingleEventOfType(.Value, withBlock: { (snapshot) in
        var dbFollowing: NSMutableArray! = snapshot.value!["Following"] as! NSMutableArray!
        dbFollowing?.addObject(userToFollow.uid)
        self.database.child("users/"+(user.uid)+"/").updateChildValues(["Following":dbFollowing!])
        //add user uid to userToFollows followers array in similar way
    }) { (error) in
        print("follow - data could not be retrieved - EXCEPTION: " + error.localizedDescription)
    }
}

This retrieves the array of from Firebase node Following, adds the uid of userToFollow, and posts the new array to node Following. This has a few problems:

1. It is not synchronized so if it is called at the same time on two devices one array will overwrite the other and followers will not be saved.
2. If there are no followers it cannot deal with a nil array, the program will crash (not the main concern, I can probably address with optionals).

I was wondering what the best practice might be to created a synchronized array of uid/tokens for user followers or post likes. I found the following links, but none seem to directly address my problem and seem to carry other problems with it. I figured it would be wise to ask the community with experience instead of Frankensteining a bunch of solutions together.

https://firebase.googleblog.com/2014/05/handling-synchronized-arrays-with-real.html https://firebase.google.com/docs/database/ios/save-data (the save data as transaction section)

Thanks for your help!

Thanks to Frank, I figured out a solution using runTransactionBlock. Here it is:

static func follow(user: FIRUser, userToFollow: FIRUser) {
    self.database.child("users/"+(user.uid)+"/Following").runTransactionBlock({ (currentData: FIRMutableData!) -> FIRTransactionResult in
        var value = currentData?.value as? Array<String>
        if (value == nil) {
            value = [userToFollow.uid]
        } else {
            if !(value!.contains(userToFollow.uid)) {
                value!.append(userToFollow.uid)
            }
        }
        currentData.value = value!
        return FIRTransactionResult.successWithValue(currentData)
        }) { (error, committed, snapshot) in
            if let error = error {
            print("follow - update following transaction - EXCEPTION: " + error.localizedDescription)
        }
    }
}

This adds the uid of userToFollow to the array Following of user. It can handle nil values and will initialize accordingly, as well as will disregard the request if the user is already following the uid of userToFollow. Let me know if you have any questions!

Some useful links:

1. The comments of firebase runTransactionBlock
2. The answer to Upvote/Downvote system within Swift via Firebase
3. The second link I posted above

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