如何阅读firebase数据库 [英] how to read firebase database

问题描述

这是我的数据结构：很多俱乐部，每个俱乐部都有地址。我试图使数据库持平。

现在我想在表格视图中加载一些俱乐部信息。当我向下滑动iPhone屏幕时，它会加载下一个俱乐部信息。

这是我的代码。但它加载所有俱乐部信息。

  func loadClubs（）{$>如何加载只有几个俱乐部，并加载下一个俱乐部时用户刷卡？ b 
 $ b ref = Database.database（）。reference（）
 
 ref.child（club）。observe（DataEventType.value，with：{（snapshot）in 
 $打印（俱乐部：\（快照））
让数组：NSArray = snapshot.children.allObjects作为NSArray 
为数组obj {b $ b让快照：DataSnapshot = obj as！DataSnapshot 
如果让childSnapshot = snapshot.value as？[String：AnyObject] {
如果让clubName = childSnapshot [name] as？String {
 print（clubName）
 
 
 
 $）
 
 
 
 
 $ Firebase的查询支持分页，但与您以前的版本稍有不同。取而代之的是使用偏移量，Firebase使用所谓的锚点值来确定从何处开始。
 
 
 
获取第一页的内容很简单，只需指定一个限制
 
 $ $ $ $ c $ ref = Database.database（）。reference（）
 query = ref。 child（club）。queryOrderedByKey（）。limitToFirst（10）
 
 query.observe（DataEventType.value，其中：{（snapshot）in 
  / pre> 
 
 
现在在该块中，跟踪您向用户展示的最后一个项目的关键字：
 对于数组obj {
 let snapshot：DataSnapshot = obj as！DataSnapshot 
如果让childSnapshot = snapshot.value as？[String：AnyObject] { 
 lastKey = childSnapshot.key 
如果让clubName = childSnapshot [name] as？String {$ b $ print（clubName）
} 
} 
} 
  
然后下一步页面，构建一个查询，从你看到的最后一个键开始： 
 
 
  query = ref.child（club） .queryOrderedByKey（）。startAt（lastKey）.limitToFirst（11）
  
您需要检索一个更多的项目比你的页面大小，因为在两个页面检索锚项目。
 
This is my data structure: many clubs, each club has address. I tried to make the database flat.

Now I want to load a few club info on table view. When I swipe down iPhone screen, it will load next a few club info.



This is my code. But it loads all club info. How can I load only a few club, and load next a few club when user swipe down?
func loadClubs() {

        ref = Database.database().reference()

        ref.child("club").observe(DataEventType.value, with: { (snapshot) in
            //print("clubs: \(snapshot)")
            let array:NSArray = snapshot.children.allObjects as NSArray
            for obj in array {
                let snapshot:DataSnapshot = obj as! DataSnapshot
                if let childSnapshot = snapshot.value as? [String: AnyObject] {
                    if let clubName = childSnapshot["name"] as? String {
                        print(clubName)
                    }
                }
            }
        })

    }

解决方案
Firebase's queries support pagination, but it's slightly different from what you're used to. Instead of working with offsets, Firebase uses so-called anchor values to determine where to start.

Getting the items for the first page is easy, you just specify a limit to the number of items to retrieve:
    ref = Database.database().reference()
    query = ref.child("club").queryOrderedByKey().limitToFirst(10)

    query.observe(DataEventType.value, with: { (snapshot) in
Now within the block, keep track of the key of the last item you've shown to the user:
   for obj in array {
        let snapshot:DataSnapshot = obj as! DataSnapshot
        if let childSnapshot = snapshot.value as? [String: AnyObject] {
            lastKey = childSnapshot.key
            if let clubName = childSnapshot["name"] as? String {
                print(clubName)
            }
        }
    }
Then to get the next page, construct a query that starts at the last key you've seen:
    query = ref.child("club").queryOrderedByKey().startAt(lastKey).limitToFirst(11)
You'll need to retrieve one more item than your page size, since the anchor item is retrieve in both pages.

                        
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