Question

我有一个像这样的Firebase结构：

...    
  "objects" : {
    "-M2ToRL-DOIL5B7Kq1JH" : {
      "name" : "Orange",
      "weight" : 50,
      "color" : "Orange",
      "objectID" : "-M2ToRL-DOIL5B7Kq1JH"
    },
    "-M2U20-rpaaWBWnXjirx" : {
       "name" : "Banana",
      "weight" : 20,
      "color" : "Yellow",
      "objectID" : "-M2U20-rpaaWBWnXjirx"
    }
  },

我想访问childByAutoID键。我有这样的查询，但没有任何结果。

ref?.child("objects").queryOrdered(byChild:"name").queryEqual(toValue: name).observeSingleEvent(of: .value, with: { (snapshot) in

                if snapshot.exists() {
                    print(snapshot)
                    let value = snapshot.value as? NSDictionary
                    var key = ""
                    key = value?["objectID"] as? String ?? "Error"

                } else {

                    return
                }

            }, withCancel: {(Error) in
                print(Error.localizedDescription)
            })

我也尝试获取value.key，但未成功。我如何从孩子本身或从存储的objectID值中获取密钥？

Answer 1

如果要检索值"-M2ToRL-DOIL5B7Kq1JH"，则需要迭代访问它：

ref?.child("objects").queryOrdered(byChild:"name").queryEqual(toValue: name).observeSingleEvent(of: .value, with: { (snapshot) in
             for child in snapshot.children.allObjects as! [DataSnapshot]{
                print(child.key);
                if snapshot.exists() {
                    print(snapshot)
                    let value = snapshot.value as? NSDictionary
                    var key = ""
                    key = value?["objectID"] as? String ?? "Error"

                } else {

                    return
                }
             }

            }, withCancel: {(Error) in
                print(Error.localizedDescription)
            })

由于您的引用位于节点objects上，因此要访问键，请使用for循环，然后使用属性key

在此处查看更多信息：

https://firebase.google.com/docs/reference/swift/firebasedatabase/api/reference/Classes/DataSnapshot#key

Answer 2

如果您将childByAutoId用作密钥，通常没有理由在节点内复制该数据，因为您可以直接访问密钥。

例如

ref?.child("objects").queryOrdered(byChild:"name").queryEqual(toValue: name).observeSingleEvent(of: .value, with: { snapshot in
    if snapshot.exists() == false {
        print("none found, returning")
        return
    }

    let allResults = snapshot.children.allObjects as! [DataSnapshot]
    for snap in allResults {
        print(snap.key) //prints each child key
    }

从子级访问childByAutoID密钥

2 个答案: