Firebase Cloud Functions：如何从“change”和“context”获取数据？

Question

在火力地堡SDK云功能迁移指南：测试版到1.0版文档中说，云计算功能的触发onUpdate参数现在(change, context)。如果我登录，change我会得到一个对象：

Change {
  before: 
   QueryDocumentSnapshot {
     _ref: DocumentReference { _firestore: [Object], _referencePath: [Object] },
     _fieldsProto: { word: [Object] },
     _readTime: undefined,
     _createTime: '2018-04-10T15:37:11.775234000Z',
     _updateTime: '2018-04-10T15:58:06.388975000Z' },
  after: 
   QueryDocumentSnapshot {
     _ref: DocumentReference { _firestore: [Object], _referencePath: [Object] },
     _fieldsProto: { word: [Object] },
     _readTime: undefined,
     _createTime: '2018-04-10T15:37:11.775234000Z',
     _updateTime: '2018-04-10T15:58:06.388975000Z' } }

文档说我可以使用change.before.val()和从此对象获取数据change.after.val()。但记录change.before.val()导致此错误消息：

TypeError: change.before.val is not a function

日志记录change.after.val()产生此错误消息：

TypeError: Cannot read property 'val' of undefined

context在这个对象中记录结果，它不包括我想要的数据：

{ eventId: 'a981ffc3-a07a-4b17-8698-0f3ef6207ced-0',
  timestamp: '2018-04-10T17:03:00.699887Z',
  eventType: 'google.firestore.document.update',
  resource: 
   { service: 'firestore.googleapis.com',
     name: 'projects/languagetwo-cd94d/databases/(default)/documents/Oxford_Dictionaries/Word_Request' },
  params: { Word_Request: 'Word_Request' } }

这些(change, context)参数是否仅适用于实时数据库而不适用于 Cloud Firestore？

这是我的代码：

exports.oxfordPronunciation = functions.firestore.document('Oxford_Dictionaries/{Word_Request}').onUpdate((change, context) => {

console.log(change);

  let options = {
    url: 'https://od-api.oxforddictionaries.com/api/v1/entries/en/ace/pronunciations%3B%20regions%3Dus',
    headers: {
      'app_id': 'TDK',
      'app_key': 'swordfish'
    }
  };

  function callback(error, response, body) {
    if (!error && response.statusCode == 200) {
      var word = JSON.parse(body);
      admin.firestore().collection('Oxford_Dictionaries').doc('Word_Response').set({ 'token': word });
    }
  }

  request(options, callback);
  return 0;
});

这是我的节点模块：

npm list --depth=0 
functions@ /Users/TDK/LanguageTwo/functions
??? firebase-admin@5.12.0
??? firebase-functions@1.0.1
??? request@2.85.0

Answer 1

在Firestore 中，您需要使用data()而不是val()：

exports.dbWrite = functions.firestore.document('/path').onWrite((change, context) => {
const beforeData = change.before.data(); // data before the write
const afterData = change.after.data(); // data after the write
});