IO-3166-Global-Notifications-Part-2 - Checkpoint

client/src/utils/GraphQLClient.js

@@ -143,7 +143,41 @@ middlewares.push(
   new SentryLink().concat(roundTripLink.concat(retryLink.concat(errorLink.concat(authLink.concat(link)))))
 );
 
-const cache = new InMemoryCache({});
+const cache = new InMemoryCache({
+  typePolicies: {
+    Query: {
+      fields: {
+        // Note: This is required because we switch from a read to an unread state with a toggle,
+        notifications: {
+          merge(existing = [], incoming = [], { readField }) {
+            // Create a map to deduplicate by __ref
+            const merged = new Map();
+
+            // Add existing items to retain cached data
+            existing.forEach((item) => {
+              const ref = readField("__ref", item);
+              if (ref) {
+                merged.set(ref, item);
+              }
+            });
+
+            // Add incoming items, overwriting duplicates
+            incoming.forEach((item) => {
+              const ref = readField("__ref", item);
+              if (ref) {
+                merged.set(ref, item);
+              }
+            });
+
+            // Return incoming to respect the current query’s filter (e.g., unread-only or all)
+            return incoming;
+          }
+        }
+      }
+    }
+  }
+});
+
 const client = new ApolloClient({
   link: ApolloLink.from(middlewares),
   cache,
@@ -163,4 +197,5 @@ const client = new ApolloClient({
     }
   }
 });
+
 export default client;