⚡ Bolt: Eliminate redundant API request by deriving lists in-memory

.jules/bolt.md

@@ -5,3 +5,7 @@
 ## 2024-05-18 - Concurrent Fetching with Owner IDs in Share Links
 **Learning:** In the share system, endpoints processing a share code typically suffer from waterfall latency by first loading target entity details (like a project) and then querying its associated elements (like project lists) using the entity's owner ID (`userId`). However, the `shareLink` object already contains the `userId` field (representing the owner's ID).
 **Action:** Always leverage the existing owner's ID within `shareLink` to bypass sequential dependencies and fetch parent entities (like projects) concurrently with their child elements (like user lists) using `Promise.all`.
+
+## 2024-05-19 - Derive Subsets In-Memory to Reduce API Calls
+**Learning:** Requesting a global collection (e.g., all lists for a user) and a subset of that same collection (e.g., lists for a specific project) as separate API calls creates redundant backend database queries and increases network payload unnecessarily.
+**Action:** When both a global collection and its subset are needed on the frontend simultaneously, fetch only the global collection and derive the subset in-memory using array filtering. This eliminates redundant API endpoints and backend load.

src/app/projects/[id]/page.tsx

@@ -58,17 +58,17 @@ export default function ProjectDetailPage({ params }: { params: Promise<{ id: st
       setIsLoading(true);
 
       // OPTIMIZATION: Execute independent network requests and JSON parsing concurrently
-      // using Promise.all. This prevents a 3-step waterfall, reducing Time to First Byte
+      // using Promise.all. This prevents a waterfall, reducing Time to First Byte
       // (TTFB) and overall load time significantly on this detail page.
-      const [projectRes, listsRes, allListsRes] = await Promise.all([
+      // We fetch the project details and all the user's lists, deriving the project
+      // lists in-memory to prevent a redundant backend query.
+      const [projectRes, allListsRes] = await Promise.all([
         fetch(`/api/projects/${projectId}`),
-        fetch(`/api/projects/${projectId}/lists`),
         fetch("/api/lists"),
       ]);
 
-      const [projectResult, listsResult, allListsResult] = await Promise.all([
+      const [projectResult, allListsResult] = await Promise.all([
         projectRes.json(),
-        listsRes.json(),
         allListsRes.json(),
       ]);
 
@@ -81,12 +81,10 @@ export default function ProjectDetailPage({ params }: { params: Promise<{ id: st
       setEditName(projectResult.data.name);
       setEditDescription(projectResult.data.description || "");
 
-      if (listsResult.success) {
-        setLists(listsResult.data);
-      }
-
       if (allListsResult.success) {
         setAllLists(allListsResult.data);
+        // Derive the project-specific lists in-memory
+        setLists(allListsResult.data.filter((list: List) => list.projectId === projectId));
       }
     } catch (err) {
       console.error("Error fetching project:", err);