Allow for providing a fetchPolicy to ObservableQuery.fetchResults

Author: kvenn

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

@@ -182,12 +182,18 @@ class ObservableQuery<TParsed> {
     }
   }
 
-  /// Fetch results based on [options.fetchPolicy]
+  /// Fetch results based on [options.fetchPolicy] by default.
+  ///
+  /// Optionally provide a [fetchPolicy] which will override the
+  /// default [options.fetchPolicy], just for this request.
   ///
   /// Will [startPolling] if [options.pollInterval] is set
-  MultiSourceResult<TParsed> fetchResults() {
+  MultiSourceResult<TParsed> fetchResults({FetchPolicy? fetchPolicy}) {
+    final fetchOptions = fetchPolicy == null 
+      ? options 
+      : options.copyWithFetchPolicy(fetchPolicy);
     final MultiSourceResult<TParsed> allResults =
-        queryManager.fetchQueryAsMultiSourceResult(queryId, options);
+        queryManager.fetchQueryAsMultiSourceResult(queryId, fetchOptions);
     latestResult ??= allResults.eagerResult;
 
     if (allResults.networkResult == null) {
@@ -201,8 +207,8 @@ class ObservableQuery<TParsed> {
           : QueryLifecycle.pending;
     }
 
-    if (options.pollInterval != null && options.pollInterval! > Duration.zero) {
-      startPolling(options.pollInterval);
+    if (fetchOptions.pollInterval != null && fetchOptions.pollInterval! > Duration.zero) {
+      startPolling(fetchOptions.pollInterval);
     }
 
     return allResults;