feat: Add ParseQuery.watch to trigger LiveQuery only on update of s…

…pecific fields (parse-community#8028)

spec/ParseLiveQuery.spec.js

@@ -394,6 +394,49 @@ describe('ParseLiveQuery', function () {
     await object.save();
   });
 
+  xit('can handle live query with fields - enable upon JS SDK support', async () => {
+    await reconfigureServer({
+      liveQuery: {
+        classNames: ['Test'],
+      },
+      startLiveQueryServer: true,
+    });
+    const query = new Parse.Query('Test');
+    query.watch('yolo');
+    const subscription = await query.subscribe();
+    const spy = {
+      create(obj) {
+        if (!obj.get('yolo')) {
+          fail('create should not have been called');
+        }
+      },
+      update(object, original) {
+        if (object.get('yolo') === original.get('yolo')) {
+          fail('create should not have been called');
+        }
+      },
+    };
+    const createSpy = spyOn(spy, 'create').and.callThrough();
+    const updateSpy = spyOn(spy, 'update').and.callThrough();
+    subscription.on('create', spy.create);
+    subscription.on('update', spy.update);
+    const obj = new Parse.Object('Test');
+    obj.set('foo', 'bar');
+    await obj.save();
+    obj.set('foo', 'xyz');
+    obj.set('yolo', 'xyz');
+    await obj.save();
+    const obj2 = new Parse.Object('Test');
+    obj2.set('foo', 'bar');
+    obj2.set('yolo', 'bar');
+    await obj2.save();
+    obj2.set('foo', 'bart');
+    await obj2.save();
+    await new Promise(resolve => setTimeout(resolve, 2000));
+    expect(createSpy).toHaveBeenCalledTimes(1);
+    expect(updateSpy).toHaveBeenCalledTimes(1);
+  });
+
   it('can handle afterEvent set pointers', async done => {
     await reconfigureServer({
       liveQuery: {

spec/ParseLiveQueryServer.spec.js

@@ -1087,6 +1087,61 @@ describe('ParseLiveQueryServer', function () {
     done();
   });
 
+  it('can handle create command with watch', async () => {
+    jasmine.restoreLibrary('../lib/LiveQuery/Client', 'Client');
+    const Client = require('../lib/LiveQuery/Client').Client;
+    const parseLiveQueryServer = new ParseLiveQueryServer({});
+    // Make mock request message
+    const message = generateMockMessage();
+
+    const clientId = 1;
+    const parseWebSocket = {
+      clientId,
+      send: jasmine.createSpy('send'),
+    };
+    const client = new Client(clientId, parseWebSocket);
+    spyOn(client, 'pushCreate').and.callThrough();
+    parseLiveQueryServer.clients.set(clientId, client);
+
+    // Add mock subscription
+    const requestId = 2;
+    const query = {
+      className: testClassName,
+      where: {
+        key: 'value',
+      },
+      watch: ['yolo'],
+    };
+    await addMockSubscription(parseLiveQueryServer, clientId, requestId, parseWebSocket, query);
+    // Mock _matchesSubscription to return matching
+    parseLiveQueryServer._matchesSubscription = function (parseObject) {
+      if (!parseObject) {
+        return false;
+      }
+      return true;
+    };
+    parseLiveQueryServer._matchesACL = function () {
+      return Promise.resolve(true);
+    };
+
+    parseLiveQueryServer._onAfterSave(message);
+
+    // Make sure we send create command to client
+    await timeout();
+
+    expect(client.pushCreate).not.toHaveBeenCalled();
+
+    message.currentParseObject.set('yolo', 'test');
+    parseLiveQueryServer._onAfterSave(message);
+
+    await timeout();
+
+    const args = parseWebSocket.send.calls.mostRecent().args;
+    const toSend = JSON.parse(args[0]);
+    expect(toSend.object).toBeDefined();
+    expect(toSend.original).toBeUndefined();
+  });
+
   it('can match subscription for null or undefined parse object', function () {
     const parseLiveQueryServer = new ParseLiveQueryServer({});
     // Make mock subscription

src/LiveQuery/ParseLiveQueryServer.js

@@ -22,6 +22,7 @@ import { getCacheController, getDatabaseController } from '../Controllers';
 import LRU from 'lru-cache';
 import UserRouter from '../Routers/UsersRouter';
 import DatabaseController from '../Controllers/DatabaseController';
+import { isDeepStrictEqual } from 'util';
 
 class ParseLiveQueryServer {
   clients: Map;
@@ -329,6 +330,10 @@ class ParseLiveQueryServer {
             } else {
               return null;
             }
+            const watchFieldsChanged = this._checkWatchFields(client, requestId, message);
+            if (!watchFieldsChanged && (type === 'update' || type === 'create')) {
+              return;
+            }
             res = {
               event: type,
               sessionToken: client.sessionToken,
@@ -707,6 +712,17 @@ class ParseLiveQueryServer {
     return auth;
   }
 
+  _checkWatchFields(client: any, requestId: any, message: any) {
+    const subscriptionInfo = client.getSubscriptionInfo(requestId);
+    const watch = subscriptionInfo?.watch;
+    if (!watch) {
+      return true;
+    }
+    const object = message.currentParseObject;
+    const original = message.originalParseObject;
+    return watch.some(field => !isDeepStrictEqual(object.get(field), original?.get(field)));
+  }
+
   async _matchesACL(acl: any, client: any, requestId: number): Promise<boolean> {
     // Return true directly if ACL isn't present, ACL is public read, or client has master key
     if (!acl || acl.getPublicReadAccess() || client.hasMasterKey) {
@@ -888,6 +904,9 @@ class ParseLiveQueryServer {
       if (request.query.fields) {
         subscriptionInfo.fields = request.query.fields;
       }
+      if (request.query.watch) {
+        subscriptionInfo.watch = request.query.watch;
+      }
       if (request.sessionToken) {
         subscriptionInfo.sessionToken = request.sessionToken;
       }