feat(client): only rebroadcast on deep equals

packages/graphql/lib/src/core/query_manager.dart

@@ -1,6 +1,7 @@
 import 'dart:async';
 
 import 'package:meta/meta.dart';
+import 'package:collection/collection.dart';
 
 import 'package:gql_exec/gql_exec.dart';
 import 'package:gql_link/gql_link.dart' show Link;
@@ -17,10 +18,14 @@ import 'package:graphql/src/scheduler/scheduler.dart';
 
 import 'package:graphql/src/core/_query_write_handling.dart';
 
+bool Function(dynamic a, dynamic b) _deepEquals =
+    const DeepCollectionEquality().equals;
+
 class QueryManager {
   QueryManager({
     @required this.link,
     @required this.cache,
+    this.alwaysRebroadcast = false,
   }) {
     scheduler = QueryScheduler(
       queryManager: this,
@@ -30,6 +35,9 @@ class QueryManager {
   final Link link;
   final GraphQLCache cache;
 
+  /// Whether to skip deep equality checks in [maybeRebroadcastQueries]
+  final bool alwaysRebroadcast;
+
   QueryScheduler scheduler;
   int idCounter = 1;
 
@@ -384,11 +392,11 @@ class QueryManager {
 
     for (ObservableQuery query in queries.values) {
       if (query != exclude && query.isRebroadcastSafe) {
-        final dynamic cachedData = cache.readQuery(
+        final cachedData = cache.readQuery(
           query.options.asRequest,
           optimistic: true,
         );
-        if (cachedData != null) {
+        if (_cachedDataHasChangedFor(query, cachedData)) {
           query.addResult(
             mapFetchResultToQueryResult(
               Response(data: cachedData),
@@ -403,6 +411,13 @@ class QueryManager {
     return true;
   }
 
+  bool _cachedDataHasChangedFor(
+    ObservableQuery query,
+    Map<String, dynamic> cachedData,
+  ) =>
+      cachedData != null &&
+      (alwaysRebroadcast || !_deepEquals(query.latestResult.data, cachedData));
+
   void setQuery(ObservableQuery observableQuery) {
     queries[observableQuery.queryId] = observableQuery;
   }

packages/graphql/lib/src/graphql_client.dart

@@ -12,6 +12,10 @@ import 'package:graphql/src/core/fetch_more.dart';
 /// The link is a [Link] over which GraphQL documents will be resolved into a [Response].
 /// The cache is the [GraphQLCache] to use for caching results and optimistic updates.
 ///
+/// The client automatically rebroadcasts watched queries when their underlying data
+/// changes in the cache. To skip the data comparison check, `alwaysRebroadcast: true` can be passed.
+/// **NOTE**: This flag was added ot accomodate the old default behavior.
+/// It is marked `@experimental` because it may be deprecated in the future.
 ///
 /// [ac]: https://www.apollographql.com/docs/react/v3.0-beta/api/core/ApolloClient/
 /// [link]: https://github.com/gql-dart/gql/tree/master/links/gql_link
@@ -21,11 +25,13 @@ class GraphQLClient implements GraphQLDataProxy {
     @required this.link,
     @required this.cache,
     this.defaultPolicies,
+    @experimental bool alwaysRebroadcast = false,
   }) {
     defaultPolicies ??= DefaultPolicies();
     queryManager = QueryManager(
       link: link,
       cache: cache,
+      alwaysRebroadcast: alwaysRebroadcast ?? false,
     );
   }