如何使用顺序 ID 从 Firebase 检索随机对象？

Question

我正在寻找一种简单的方法来使用 swift 在 Firebase 中查询我的数据库以检索随机对象。我已经阅读了很多线程，似乎没有一个简单的方法。一个例子表明可以通过创建一个序列号来完成，但是没有关于如何为每条记录创建这个序列号的信息。

因此，要么我需要有关如何在每次创建记录时创建序列号的信息，要么是否有人知道一种从数据库中检索随机记录的简单方法，这将非常有帮助。最好是迅速。

我的数据库结构：

Answer 1

在 Firebase 中查询随机对象 SWIFT 4

您可以尝试的一件事是像这样重构您的数据：

    - profiles
       - 1jon2jbn1ojb3pn231 //Auto-generated id from firebase.
          - jack@hotmail.com
       - oi12y3o12h3oi12uy3 //Auto-generated id from firebase.
          - susan@hotmail.com
       - ...

Firebase 的自动生成的 id 在发送到 Firebase 时按字典顺序按键排序，因此您可以轻松创建如下函数：

    func createRandomIndexForFirebase() -> String {
        let randomIndexArray = ["a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z","0","1","2","3","4","5","6","7","8","9"]`
        let randomIndex = Int.random(in: 0..<randomIndexArray.endIndex)

        //In lexicographical order 'A' != 'a' so we use some clever logic to randomize the case of any letter that is chosen.
        //If a numeric character is chosen, .capitalized will fail silently.
        return (randomIndex % 2 == 0) ? randomIndexArray[randomIndex] : randomIndexArray[randomIndex].capitalized 
    }

获得随机索引后，您可以创建 Firebase 查询以获取随机配置文件。

    var ref: DatabaseReference? = Database.database().reference(fromURL: "<DatabaseURL>")
    ref?.child("profiles").queryOrderedByKey().queryStarting(atValue: createRandomIndexForFirebase()).queryLimited(toFirst: 1).observeSingleEvent(of: .value, with: { snapshot in
    //Use a for-loop in case you want to set .queryLimited(toFirst: ) to some higher value.
    for snap in snapshot.children { 
      guard let randomProfile = snap as? DataSnapshot else { return }
      //Do something with your random profiles :)
    }

}

Answer 2

Database.database().reference().child("profiles").observeSingleEvent(of: .value) { (snapshot) in 
    if let snapshots = snapshot.children.allObjects as? [DataSnapshot] { 
        // do random number calculation
         let count = snapshots.count
         return snapshots[Int(arc4random_uniform(UInt32(count - 1)))]
}