Swift 3和Firebase:从快照中检索自动ID值

Question

我在firebase上创建了下面的结构,我需要用红色下划线自动id:

我创建的用于查询值的代码:

let query = reference.queryOrdered(byChild: "receiverId").queryEqual(toValue: "LKupL7KYiedpr6uEizdCapezJ6i2")
        //Start process
        query.observe(.value, with: { (snapshot) in
            guard snapshot.exists() else{
                print("Data doesn't exists")
                return
            }
            print(snapshot.key)
}

我的" snapshot.value "导致:

Optional({
    "-KaRVjQgfFD00GXurK9m" =     {
        receiverId = LKupL7KYiedpr6uEizdCapezJ6i2;
        senderId = bS6JPkEDXIVrlYtSeQQgOjCNTii1;
        timestamp = 1484389589738;
    };
})

如何从上面的节点只获得字符串-KaRVjQgfFD00GXurK9m？

我曾尝试使用" print(snapshot.key) ",但结果是用户ID: bS6JPkEDXIVrlYtSeQQgOjCNTii1

一些想法？非常感谢你.

Answer 1

.value返回父节点和满足查询结果的所有子节点.在这种情况下,需要迭代子节点(可能有多个子节点与查询匹配).

snapshot.key是父节点键(bS6JPkEDXIVrlYtSeQQgOjCNTii1),值是所有子节点的快照(字典).这些孩子中的每一个都是一个关键:uid的值对:值和值是子节点的字典,receiverId,senderId等

此代码将打印每个子节点的uid以及与查询匹配的每个用户节点的值(timestamp)之一.

    let usersRef = ref.child("users")
    let queryRef = usersRef.queryOrdered(byChild: "receiverId")
                           .queryEqual(toValue: "LKupL7KYiedpr6uEizdCapezJ6i2")

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

        for snap in snapshot.children {
            let userSnap = snap as! FIRDataSnapshot
            let uid = userSnap.key //the uid of each user
            let userDict = userSnap.value as! [String:AnyObject]
            let timestamp = userDict["timestamp"] as! String
            print("key = \(uid) and timestamp = \(timestamp)")
        } 
    })