Firebase按顺序获取数据

Question

我正在使用Firebase，直到最近我都没有按字母顺序获取数据的问题。我从来没有使用过查询，我总是只使用数据快照并逐一对其进行排序。最近，在
snapVal中 ，数据并不总是按字母顺序 排列
。如何做到这一点，以便获得按字母顺序排序的数据的snapVal，就像数据库快照中的快照一样？

真实示例：有4条消息，id1-id4（按此顺序）。它们包含消息“ 1”-“
4”。快照看起来正确。但是snapVal（snapshot.value）看起来像这样：

["id2": {
    DATE = "10/20/16";
    "FIRST_NAME" = first;
    ID = userID;
    "LAST_NAME" = last;
    MESSAGE = 2;
    TIME = "8:12 PM";
}, "id4": {
    DATE = "10/20/16";
    "FIRST_NAME" = first;
    ID = userID;
    "LAST_NAME" = last;
    MESSAGE = 4;
    TIME = "8:12 PM";
}, "id1": {
    DATE = "10/20/16";
    "FIRST_NAME" = first;
    ID = userID;
    "LAST_NAME" = last;
    MESSAGE = 1;
    TIME = "8:12 PM";
}, "id3": {
    DATE = "10/20/16";
    "FIRST_NAME" = first;
    ID = userID;
    "LAST_NAME" = last;
    MESSAGE = 3;
    TIME = "8:12 PM";
}]

快照如下所示：

["id1": {
    DATE = "10/20/16";
    "FIRST_NAME" = first;
    ID = userID;
    "LAST_NAME" = last;
    MESSAGE = 1;
    TIME = "8:12 PM";
}, "id2": {
    DATE = "10/20/16";
    "FIRST_NAME" = first;
    ID = userID;
    "LAST_NAME" = last;
    MESSAGE = 2;
    TIME = "8:12 PM";
}, "id3": {
    DATE = "10/20/16";
    "FIRST_NAME" = first;
    ID = userID;
    "LAST_NAME" = last;
    MESSAGE = 3;
    TIME = "8:12 PM";
}, "id4": {
    DATE = "10/20/16";
    "FIRST_NAME" = first;
    ID = userID;
    "LAST_NAME" = last;
    MESSAGE = 4;
    TIME = "8:12 PM";
}]

要获取snapVal，请使用以下代码：

if let snapVal = snapshot.value as? [String: AnyObject] {
     // Comes out of order..
}

澄清：

快照（最终结果正确无误）：

Snap (CHAT) {
    id1 =     {
        DATE = "10/20/16";
        "FIRST_NAME" = first;
        ID = userID;
        "LAST_NAME" = last;
        MESSAGE = 1;
        TIME = "8:12 PM";
    };
    id2 =     {
        DATE = "10/20/16";
        "FIRST_NAME" = first;
        ID = userID;
        "LAST_NAME" = last;
        MESSAGE = 2;
        TIME = "8:12 PM";
    };
    id3 =     {
        DATE = "10/20/16";
        "FIRST_NAME" = first;
        ID = userID;
        "LAST_NAME" = last;
        MESSAGE = 3;
        TIME = "8:12 PM";
    };
    id4 =     {
        DATE = "10/20/16";
        "FIRST_NAME" = first;
        ID = userID;
        "LAST_NAME" = last;
        MESSAGE = 4;
        TIME = "8:12 PM";
    };
}

这是print(snapVal.keys)inside 的输出if let snapVal = snapshot.value as? [String: AnyObject]：

LazyMapCollection<Dictionary<String, AnyObject>, String>(_base: ["id2": {
    DATE = "10/20/16";
    "FIRST_NAME" = first;
    ID = userID;
    "LAST_NAME" = last;
    MESSAGE = 2;
    TIME = "8:12 PM";
}, "id4": {
    DATE = "10/20/16";
    "FIRST_NAME" = first;
    ID = userID;
    "LAST_NAME" = last;
    MESSAGE = 4;
    TIME = "8:12 PM";
}, "id1": {
    DATE = "10/20/16";
    "FIRST_NAME" = first;
    ID = userID;
    "LAST_NAME" = last;
    MESSAGE = 1;
    TIME = "8:12 PM";
}, "id3": {
    DATE = "10/20/16";
    "FIRST_NAME" = first;
    ID = userID;
    "LAST_NAME" = last;
    MESSAGE = 3;
    TIME = "8:12 PM";
}], _transform: (Function))

我的代码：

  self.firebase.child("Chats").child(chatID).queryOrderedByKey().observeSingleEvent(of: .value, with: { (snapshot) in
                          print(snapshot)
                        if let snapVal = snapshot.value as? [String: AnyObject] {

                            print(snapVal)

                            for c in snapVal {
                                print("checking Message as child")
                                let message = c.value["MESSAGE"] as? String

                                let fn = c.value["FIRST_NAME"] as? String
                                let ln = c.value["LAST_NAME"] as? String

                                let USER_ID = c.value["ID"] as? String

                                if let userID = USER_ID {
                                    if let msg = message {
                                        if let firstName = fn {
                                            if let lastName = ln {
                                                let username = "\(firstName) \(lastName)"
                                                self.addMessage(userID, text: msg, name: username)

                                                print("Message added! \nMessage Info:")
                                                print("User ID: \(userID)")
                                                print("text: \(msg)")
                                                print("Username: \(username)")
                                            } else {
                                                print("LN did not pass")
                                            }
                                        } else {
                                            print("FN did not pass")
                                        }
                                    } else {
                                        print("Msg did not pass")
                                    }
                                } else {
                                    print("User ID did not pass")
                                }
                            }
                          }  
})

Answer 1

解决方案
：经过非常广泛的搜索和尝试后，问题仍然存在，一旦将快照转换为snapVal（snapshot.value），该顺序通常会重新排列。我的（有效）解决方案：

for child in snapshot.children {
let child = child as! FIRDataSnapshot
 if let childVal = child.value as? [String: AnyObject] {
    let childMessage = childVal["MESSAGE"] as! String
    // more code for each child. This child might be a post of a sort, which you can access properties of in a way like I did in the line above
 }
}

工艺流程 ：

1. 遍历快照中的每个孩子

2. 将子级转换为FIRDataSnapshot，因此它不是元素

3. 获取特定子项的值以从中访问属性

4. 遵循NSDictionary原则为孩子添加相应的代码。

为什么这个解决方案是可靠的

以正确的顺序接收快照非常简单。我遇到的问题是在获得时要以正确的顺序获取数据snapshot.value。该解决方案解决了该问题，因为仅在循环排序的快照子项时才访问每个子项的值。这使子级的顺序仍然受快照控制。

我也喜欢这种snapshot.value方法，[String: AnyObject]因为它非常接近Swift中Firebase实施的旧功能：简单而干净。我实际上认为，以这种方式使用NSDictionary实际上是从长远来看节省时间的一种方式，因为它绝不是冗长的。