Firebase计数父亲的子数 [英] Firebase count num children of parent

问题描述

我正在尝试获取js firebase中父节点的子节点数。
我想要：

I'm trying to get the number of children for a parent node in js firebase. I'd like to have:

'user': {
    '-Yuna99s993m': { count: 1},
    '-Yada99s993m': { count: 2},
}

我正在创建一个云函数巫婆，每次输入一个新节点时，它应该添加等于用户节点的numChildren的计数。

I'm creating a cloud function witch every time a new node is entered it should add count equal to numChildren of user node.

exports.setCount = functions.database.ref('/user/{userId}').onWrite(event => {
    // This doesn't work
    const count = event.data.ref.parent.numChildren();
    return event.data.ref.update({ count });
});

有什么帮助才能让这个工作？

Any help to get this working?

谢谢。

推荐答案

调用 event.data.ref.parent.numChildren（）将无效，因为 parent 是 DatabaseReference ，而 numChildren（） 在 DataSnapshot 上定义（通过将监听器附加到引用来获得）：

Calling event.data.ref.parent.numChildren() won't work, because parent is a DatabaseReference while numChildren() is defined on DataSnapshot (which you get by attaching a listener to a reference):

exports.setCount = functions.database.ref('/user/{userId}').onWrite(event => {
    return event.data.ref.parent.once("value", (snapshot) => {
      const count = snapshot.numChildren();
      return event.data.ref.update({ count });
    });
})

还有一个 子计数示例 Github回购，它完全符合您的要求：保持麻木的反击呃小孩该示例使用更有效的方法来保持计数。

There is also a child-count example in the functions-samples Github repo that does precisely what you want: keeping a counter of the number of children. That example uses a more efficient approach for keeping the count.

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