[Dashboard] Update Index Patterns when Child Index Patterns Change (#76356)

Added the ability for Dashboard to react to index pattern changes in its children's output.

Author: Dosant

src/plugins/dashboard/public/application/dashboard_app_controller.tsx

@@ -24,9 +24,18 @@ import { EuiCheckboxGroupIdToSelectedMap } from '@elastic/eui/src/components/for
 import React, { useState, ReactElement } from 'react';
 import ReactDOM from 'react-dom';
 import angular from 'angular';
+import deepEqual from 'fast-deep-equal';
 
 import { Observable, pipe, Subscription, merge } from 'rxjs';
-import { filter, map, debounceTime, mapTo, startWith, switchMap } from 'rxjs/operators';
+import {
+  filter,
+  map,
+  debounceTime,
+  mapTo,
+  startWith,
+  switchMap,
+  distinctUntilChanged,
+} from 'rxjs/operators';
 import { History } from 'history';
 import { SavedObjectSaveOpts } from 'src/plugins/saved_objects/public';
 import { NavigationPublicPluginStart as NavigationStart } from 'src/plugins/navigation/public';
@@ -279,6 +288,12 @@ export class DashboardAppController {
     const updateIndexPatternsOperator = pipe(
       filter((container: DashboardContainer) => !!container && !isErrorEmbeddable(container)),
       map(getDashboardIndexPatterns),
+      distinctUntilChanged((a, b) =>
+        deepEqual(
+          a.map((ip) => ip.id),
+          b.map((ip) => ip.id)
+        )
+      ),
       // using switchMap for previous task cancellation
       switchMap((panelIndexPatterns: IndexPattern[]) => {
         return new Observable((observer) => {
@@ -405,17 +420,29 @@ export class DashboardAppController {
               ) : null;
             };
 
-            outputSubscription = new Subscription();
-            outputSubscription.add(
-              dashboardContainer
-                .getOutput$()
-                .pipe(
-                  mapTo(dashboardContainer),
-                  startWith(dashboardContainer), // to trigger initial index pattern update
-                  updateIndexPatternsOperator
+            outputSubscription = merge(
+              // output of dashboard container itself
+              dashboardContainer.getOutput$(),
+              // plus output of dashboard container children,
+              // children may change, so make sure we subscribe/unsubscribe with switchMap
+              dashboardContainer.getOutput$().pipe(
+                map(() => dashboardContainer!.getChildIds()),
+                distinctUntilChanged(deepEqual),
+                switchMap((newChildIds: string[]) =>
+                  merge(
+                    ...newChildIds.map((childId) =>
+                      dashboardContainer!.getChild(childId).getOutput$()
+                    )
+                  )
                 )
-                .subscribe()
-            );
+              )
+            )
+              .pipe(
+                mapTo(dashboardContainer),
+                startWith(dashboardContainer), // to trigger initial index pattern update
+                updateIndexPatternsOperator
+              )
+              .subscribe();
 
             inputSubscription = dashboardContainer.getInput$().subscribe(() => {
               let dirty = false;