将数据从mongoDB同步到firebase，反之亦然-syncdatafrommongoDBtofirebaseandvice-versa

1  

Both database systems supports for some sort of operation log or trigger system. You can use these to live update changes to databases to sync them almost real time.

两个数据库系统都支持某种操作日志或触发系统。您可以使用这些对数据库进行实时更新更改，以便几乎实时同步它们。

For MongoDB

You can use Oplog to see what changes made to database (insert/update/delete) and run a suitable function to sync firebase.

您可以使用Oplog查看对数据库所做的更改（插入/更新/删除）并运行适当的函数来同步firebase。

oplog

OPLOG

A capped collection that stores an ordered history of logical writes to a MongoDB database. The oplog is the basic mechanism enabling replication in MongoDB.

一个上限集合，用于存储对MongoDB数据库的逻辑写入的有序历史记录。 oplog是在MongoDB中启用复制的基本机制。

There are small libraries that help you easily subscribe to these events.

有一些小型库可以帮助您轻松订阅这些事件。

Example (mongo-oplog)

示例（mongo-oplog）

import MongoOplog from 'mongo-oplog'
const oplog = MongoOplog('mongodb://127.0.0.1:27017/local', { ns: 'test.posts' })

oplog.tail();

oplog.on('op', data => {
  console.log(data);
});

oplog.on('insert', doc => {
  console.log(doc);
});

oplog.on('update', doc => {
  console.log(doc);
});

oplog.on('delete', doc => {
  console.log(doc.o._id);
});

For Firebase

You can use Cloud Functions. With Cloud Functions you can watch triggers like Cloud Firestore Triggers or Realtime Database Triggers and run a function to sync MongoDB database.

您可以使用云功能。使用云功能，您可以监视Cloud Firestore触发器或实时数据库触发器等触发器，并运行同步MongoDB数据库的功能。

With Cloud Functions, you can handle events in the Firebase Realtime Database with no need to update client code. Cloud Functions lets you run database operations with full administrative privileges, and ensures that each change to the database is processed individually.

借助云功能，您可以处理Firebase实时数据库中的事件，而无需更新客户端代码。云功能允许您以完全管理权限运行数据库操作，并确保单独处理对数据库的每个更改。

// Listens for new messages added to /messages/:pushId/original and creates an
// uppercase version of the message to /messages/:pushId/uppercase
exports.makeUppercase = functions.database.ref('/messages/{pushId}/original').onWrite((event) => {
  // Grab the current value of what was written to the Realtime Database.
  const original = event.data.val();
  console.log('Uppercasing', event.params.pushId, original);
  const uppercase = original.toUpperCase();
  // You must return a Promise when performing asynchronous tasks inside a Functions such as
  // writing to the Firebase Realtime Database.
  // Setting an "uppercase" sibling in the Realtime Database returns a Promise.
  return event.data.ref.parent.child('uppercase').set(uppercase);
});