您如何按时间顺序正确地从 Firebase 中订购数据 [英] How do you properly order data from Firebase chronologically

问题描述

我正在尝试从 Firebase 订购我的数据，因此最近的帖子位于顶部(如 Instagram)，但我无法使其正常工作.我应该使用服务器时间戳吗?是否有createdAt"字段?

I'm trying to order my data from Firebase so the most recent post is at the top (like Instagram), but I just can't get it to work properly. Should I be using a server timestamp? Is there a "createdAt" field?

func getPosts() {
    POST_REF.observeEventType(.Value, withBlock: { snapshot in
        guard let posts = snapshot.value as? [String : [String : String]] else {
            print("No Posts Found")
            return
        }

        Post.feed?.removeAll()
        for (postID, post) in posts {
            let newPost = Post.initWithPostID(postID, postDict: post)!
            Post.feed?.append(newPost)
        }
        Post.feed? = (Post.feed?.reverse())!
        self.tableView.reloadData()
        }, withCancelBlock: { error in
            print(error.localizedDescription)
    })
}

推荐答案

仅对数组使用 reverse() 不足以涵盖所有内容.您需要考虑不同的事情:

Using only reverse() for your array is not enough way to encompass everything. There are different things you need to think about:

• 在检索数据时限制，使用 append() 和 reverse() 以节省时间.您不需要每次都删除所有数组.

• Limit while retrieving data, use append() and then reverse() to save time. You don't need to delete all array for each time.

滚动触发器或willDisplay单元格方法加载

让我们开始吧.您可以为您的帖子创建一个子时间戳或日期/时间全局.为了提供类似 Instagram 秒、周的时间，我建议您使用 UTC 时间.所以我称之为:(timeUTC)

Let's start. You can create a child for your posts timestamp or date/time being global. To provide like Instagram seconds, weeks I advice you using UTC time. So I will call this: (timeUTC)

要对所有帖子进行排序，请使用 since1970 时间戳.所以我将称之为 (timestamp) 然后你也可以保留另一个节点作为 (reversedTimestamp) 添加 - 前缀到时间戳.所以当你使用 queryOrdered 到这个节点时.您可以使用 yourQuery.queryLimited(toFirst: 5) 处理最新的 5 个帖子.

For sorting your all post, use since1970 timestamp. So I will call this (timestamp) and then also you can keep another node as (reversedTimestamp) adding - prefix to timestamp. So when you use queryOrdered to this node. You can handle latest 5 post using with yourQuery.queryLimited(toFirst: 5).

1.获取 Swift 3 中 timeUTC 节点的 UTC 日期/时间:

        let date = Date()
        let formatter = DateFormatter()
        formatter.locale = Locale(identifier: "en_US_POSIX")
        formatter.dateFormat = "yyyy-MM-dd HH:mm:ss ZZZ"
        formatter.timeZone = TimeZone(abbreviation: "UTC")
        let utcTimeZoneStr = formatter.string(from: date)

+0000 表示它是世界时，看看 http://time.is/tr/UTC

+0000 means it's universal time, look at http://time.is/tr/UTC

2. 获取 1970 年以来的时间戳，以便在 Swift 3 中对帖子进行排序:

let timestamp = (Date().timeIntervalSince1970 as NSString).doubleValue
let reversedTimestamp = -1.0 * timestamp

现在，您可以像这样将它们保存在 Firebase 帖子中.

Now, you can save them on your Firebase posts like this.

"posts" : {
    "-KHLOy5mOSq0SeB7GBXv" : {
      "timestamp": "1475858019.2306"
      "timeUTC" : "2012-02-04 12:11:56 +0000"
    },
    "-KHLrapS0wbjqPP5ZSUY" : {
      "timestamp": "1475858010.1245"
      "timeUTC" : "2014-02-04 12:11:56 +0000"
    },

我将检索 5 个 5 个帖子，所以我在 viewDidLoad 中执行 queryLimited(toFirst: 5):

I will retrieve five by five post, so I'm doing queryLimited(toFirst: 5) in viewDidLoad:

let yourQuery = ...queryOrdered(byChild: "reverseTimestamp")
                   .queryEnding(atValue: "(self.pageOnTimestamp)", childKey: "reverseTimestamp")

    yourQuery.observeSingleEvent(of: .value, with: { (snapshot) in

        if snapshot.value is NSNull {

            print("There is no post.")

        }
        else {

            yourQuery.queryLimited(toFirst: 5).observeSingleEvent(of: .value, with: { (snapshot) in

                self.posts.removeAll(keepingCapacity: true)

                for (i, snap) in snapshot.children.enumerated() {

                    if let postAllDict = snapshot.value as? [String: AnyObject] {
                        if let postDict = postAllDict[(snap as AnyObject).key as String] as? [String: AnyObject] {

                            let post = Post(key: (snap as AnyObject).key as String, postDict: postDict)
                            self.posts.append(post)
                        }
                    }
                }

                completion(true)
            })
        }
    })

如果用户到达了最新的帖子，您可以使用如下的willDisplay方法处理它，然后您可以调用loadMore函数.

If user reached latest post, you can handle it with willDisplay method like below, then you can call loadMore function.

func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {

   if self.posts.count - 1 == indexPath.row {
      // call loadMore function.
   }
}

在 loadMore() 函数中，您可以处理最新帖子的时间戳，然后开始-结束查询，这样您就可以轻松地继续下前 5 个帖子，同时追加到数组之前.

In loadMore() function you can handle latest post's timestamp, then start-end query as with that, so you can easily continue with next first 5 posts while appending before array.

对于格式良好的 Swift 3 转换，请查看此处:Swift 3 - UTC 到时间前标签，思考 12h/24h 设备时间变化

For Swift 3 conversion as nice formatted, take a look here: Swift 3 - UTC to time ago label, thinking 12h / 24h device time changes

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