How to update clients when database is edited outside of feathersjs app

I have two server-side applications editing the same database.

One server is a feathersjs app and another is a simple nodejs app. A frontend app connects to the feathersjs app via feathersjs client.

How, when the nodejs app edits the database, can I update clients connected to the feathersjs app? As currently any changes made outside the featherjs app aren't reflected on the feathersjs clients.

Can I trigger the patched event somehow and force the clients to pull down the updated data?

Solution

if you are using mongodb with WiredTiger storageEngine you can use the collection.watch() function and add a monitor in your feathers app something like this

   //src/services/monitor.js 
   module.exports = function(app){
      //get mongo client
      const mongoClient = app.get('mongoClient');
      //connect db
      mongoClient.then(db => {

        //collection to watch
        const collection = db.collection('your_collection_name')

        //watch collection
        const changeStream = collection.watch({ fullDocument: 'updateLookup' });

        //on some data changed
        changeStream.on('change', data => {
          console.log ( 'something is changed in your collection' , data )
          //your service.emit
        });
      })
    }

Then I added this simple monitor in the /src/services/index.js (maybe not the right way but it works)

//src/services/index.js
...
const monitor = require('./monitor.js');
module.exports = function (app) {
   ...
   app.configure(monitor);
   ...
};

Data returned on every change on the collection

{ _id:
   { _data:
      '825C7F03230000001C29295A100490DEF2C65812410FABF0DE46F9C89D7246645F696400645C1AC097B189CBD5D4A24D330004' },
  operationType: 'replace',
  clusterTime:
   Timestamp { _bsontype: 'Timestamp', low_: 28, high_: 1551827747 },
  fullDocument:
   { _id: 5c1ac097b189cbd5d4a24d33,
     id: '12',
     language: 'it-IT',
     category: 'some data',
     slug: '',
     description: 'some data',
     src:'',
     color: 'card',
     status: true,
     home: true,
     order_int: '3',
     visual: 'card' },
  ns: { db: 'mydb', coll: 'mycollection' },
  documentKey: { _id: 5c1ac097b189cbd5d4a24d33 } }

More info here https://docs.mongodb.com/manual/reference/method/db.collection.watch/