New onlyComplete() helper to filter only complete results

.changeset/olive-dogs-watch.md

@@ -0,0 +1,25 @@
+---
+'apollo-angular': minor
+---
+
+New `onlyComplete()` helper to filter only complete results
+
+If you use this, you should probably combine it with [`notifyOnNetworkStatusChange`](https://www.apollographql.com/docs/react/data/queries#queryhookoptions-interface-notifyonnetworkstatuschange).
+This tells `@apollo/client` to not emit the first `partial` result, so
+`apollo-angular` does not need to filter it out. The overall behavior is
+identical, but it saves some CPU cycles.
+
+So something like this:
+
+```ts
+apollo
+  .watchQuery({
+    query: myQuery,
+    notifyOnNetworkStatusChange: false, // Adding this will save CPU cycles
+  })
+  .valueChanges
+  .pipe(onlyComplete())
+  .subscribe(result => {
+    // Do something with complete result
+  });
+```

packages/apollo-angular/src/index.ts

@@ -8,3 +8,4 @@ export { Subscription } from './subscription';
 export { APOLLO_OPTIONS, APOLLO_NAMED_OPTIONS, APOLLO_FLAGS } from './tokens';
 export type { Flags, NamedOptions, ResultOf, VariablesOf } from './types';
 export { gql } from './gql';
+export { onlyComplete } from './only-complete';

packages/apollo-angular/src/only-complete.ts

@@ -0,0 +1,36 @@
+import { filter, type OperatorFunction } from 'rxjs';
+import type { ObservableQuery } from '@apollo/client/core';
+
+/**
+ * Filter emitted results to only receive results that are complete (`result.dataState === 'complete'`).
+ *
+ * This is a small wrapper around rxjs `filter()` for convenience only.
+ *
+ * If you use this, you should probably combine it with [`notifyOnNetworkStatusChange`](https://www.apollographql.com/docs/react/data/queries#queryhookoptions-interface-notifyonnetworkstatuschange).
+ * This tells `@apollo/client` to not emit the first `partial` result, so `apollo-angular` does
+ * not need to filter it out. The overall behavior is identical, but it saves some CPU cycles.
+ *
+ * So something like this:
+ *
+ * ```ts
+ * apollo
+ *   .watchQuery({
+ *     query: myQuery,
+ *     notifyOnNetworkStatusChange: false, // Adding this will save CPU cycles
+ *   })
+ *   .valueChanges
+ *   .pipe(onlyComplete())
+ *   .subscribe(result => {
+ *     // Do something with complete result
+ *   });
+ * ```
+ */
+export function onlyComplete<TData>(): OperatorFunction<
+  ObservableQuery.Result<TData>,
+  ObservableQuery.Result<TData, 'complete'>
+> {
+  return filter(
+    (result): result is ObservableQuery.Result<TData, 'complete'> =>
+      result.dataState === 'complete',
+  );
+}

packages/apollo-angular/testing/tests/only-complete.spec.ts

@@ -0,0 +1,57 @@
+import { onlyComplete } from 'apollo-angular';
+import { Subject } from 'rxjs';
+import { describe, expect, test } from 'vitest';
+import { NetworkStatus, ObservableQuery } from '@apollo/client/core';
+
+interface Result {
+  user: {
+    name: string;
+  };
+}
+
+describe('onlyComplete', () => {
+  let theUser: Result['user'] | null = null;
+  let count = 0;
+
+  test('should receive only complete results', () =>
+    new Promise<void>(done => {
+      const b = new Subject<ObservableQuery.Result<Result>>();
+      b.pipe(onlyComplete()).subscribe({
+        next: result => {
+          count++;
+          theUser = result.data.user;
+        },
+        complete: () => {
+          expect(count).toBe(1);
+          expect(theUser).toEqual({ name: 'foo' });
+          done();
+        },
+      });
+
+      b.next({
+        dataState: 'partial',
+        data: {},
+        loading: true,
+        partial: true,
+        networkStatus: NetworkStatus.loading,
+      } satisfies ObservableQuery.Result<Result, 'partial'>);
+
+      b.next({
+        dataState: 'complete',
+        data: { user: { name: 'foo' } },
+        loading: false,
+        partial: false,
+        networkStatus: NetworkStatus.ready,
+      } satisfies ObservableQuery.Result<Result, 'complete'>);
+
+      b.next({
+        dataState: 'partial',
+        data: {},
+        loading: true,
+        partial: true,
+        networkStatus: NetworkStatus.loading,
+      } satisfies ObservableQuery.Result<Result, 'partial'>);
+
+      b.complete();
+    }));
+});

packages/demo/src/app/app.component.ts

@@ -1,5 +1,8 @@
+import { Apollo, gql, onlyComplete } from 'apollo-angular';
+import { Subject } from 'rxjs';
 import { Component } from '@angular/core';
 import { RouterLink, RouterOutlet } from '@angular/router';
+import type { ObservableQuery } from '@apollo/client/core';
 
 @Component({
   selector: 'app-root',

packages/demo/src/app/pages/movie/movie-page.component.ts

@@ -1,6 +1,6 @@
-import { Apollo, gql } from 'apollo-angular';
+import { Apollo, gql, onlyComplete } from 'apollo-angular';
 import { Observable } from 'rxjs';
-import { filter, map } from 'rxjs/operators';
+import { map } from 'rxjs/operators';
 import { AsyncPipe } from '@angular/common';
 import { Component, inject, OnInit } from '@angular/core';
 import { ActivatedRoute, RouterLink } from '@angular/router';
@@ -69,10 +69,11 @@ export class MoviePageComponent implements OnInit {
         variables: {
           id: this.route.snapshot.paramMap.get('id')!,
         },
+        notifyOnNetworkStatusChange: false,
       })
       .valueChanges.pipe(
-        map(result => (result.dataState === 'complete' ? result.data.film : null)),
-        filter(Boolean),
+        onlyComplete(),
+        map(result => result.data.film),
       );
   }
 }

packages/demo/src/app/pages/movies/movies-page.component.ts

@@ -1,6 +1,6 @@
-import { Apollo, gql } from 'apollo-angular';
+import { Apollo, gql, onlyComplete } from 'apollo-angular';
 import { Observable } from 'rxjs';
-import { filter, map } from 'rxjs/operators';
+import { map } from 'rxjs/operators';
 import { AsyncPipe } from '@angular/common';
 import { Component, inject, OnInit } from '@angular/core';
 import { RouterLink } from '@angular/router';
@@ -56,10 +56,11 @@ export class MoviesPageComponent implements OnInit {
             }
           }
         `,
+        notifyOnNetworkStatusChange: false,
       })
       .valueChanges.pipe(
-        map(result => (result.dataState == 'complete' ? result.data.allFilms.films : null)),
-        filter(Boolean),
+        onlyComplete(),
+        map(result => result.data.allFilms.films),
       );
   }
 }