如何使用 Cloud Function .onWrite (Firebase) 从其他数据库节点获取变量

Question

如果 Firebase 节点设置为 true，我正在尝试设置一些要发送的变量以传递给函数。我正在尝试使用.parent 和.val() 函数来设置customer_id，基于此处的文档：https://firebase.google.com/docs/functions/database-events

exports.newCloudFunction = functions.database.ref('/user/{userId}/sources/saveSource').onWrite(event => {
// Retrieve true/false value to verify whether card should be kept on file
const saveSource = event.data.val();

if (saveSource) {
  let snap = event.data;
  let customer_id = snap.ref.parent.child('customer_id').val();
  console.log(customer_id);
  // pass customer_id into function
}

我期待 snap.ref.parent 引用 /sources 和 .child('customer_id').val() 以访问来自 customer_id 键的值。

但是，当我尝试运行此功能时，出现以下错误：

TypeError: snap.ref.parent.child(...).val is not a function
at exports.linkCardToSquareAccount.functions.database.ref.onWrite.event (/user_code/index.js:79:56)
at /user_code/node_modules/firebase-functions/lib/cloud-functions.js:35:20
at process._tickDomainCallback (internal/process/next_tick.js:129:7)

如何引用原始 onWrite 位置范围之外的节点？

Answer 1

您不能只在数据库引用上调用.val() 并期望在该位置获取数据。您需要添加一个值侦听器才能获取新数据。

幸运的是，Cloud Functions 完全支持这一点：

exports.newCloudFunction = functions.database.ref('/user/{userId}/sources/saveSource').onWrite(event => {
    // Retrieve true/false value to verify whether card should be kept on file
    const saveSource = event.data.val();

    if (saveSource) {
        const customerIdRef = event.data.adminRef.parent.child('customer_id')
        // attach a 'once' value listener to get the data at this location only once
        // this returns a promise, so we know the function won't terminate before we have retrieved the customer_id
        return customerIdRef.once('value').then(snap => {
            const customer_id = snap.val();
            console.log(customer_id);
            // use customer_id here
        });
    } 
});

您可以了解更多here。