Cursor rule

1---
2alwaysApply: false
3---
4 
5## Per-Request Deduplication with React.cache()
6 
7Use `React.cache()` for server-side request deduplication. Authentication and database queries benefit most.
8 
9**Usage:**
10 
11```typescript
12import { cache } from 'react'
13 
14export const getCurrentUser = cache(async () => {
15  const session = await auth()
16  if (!session?.user?.id) return null
17  return await db.user.findUnique({
18    where: { id: session.user.id }
19  })
20})
21```
22 
23Within a single request, multiple calls to `getCurrentUser()` execute the query only once.
24 
25**Avoid inline objects as arguments:**
26 
27`React.cache()` uses shallow equality (`Object.is`) to determine cache hits. Inline objects create new references each call, preventing cache hits.
28 
29**Incorrect (always cache miss):**
30 
31```typescript
32const getUser = cache(async (params: { uid: number }) => {
33  return await db.user.findUnique({ where: { id: params.uid } })
34})
35 
36// Each call creates new object, never hits cache
37getUser({ uid: 1 })
38getUser({ uid: 1 })  // Cache miss, runs query again
39```
40 
41**Correct (cache hit):**
42 
43```typescript
44const getUser = cache(async (uid: number) => {
45  return await db.user.findUnique({ where: { id: uid } })
46})
47 
48// Primitive args use value equality
49getUser(1)
50getUser(1)  // Cache hit, returns cached result
51```
52 
53If you must pass objects, pass the same reference:
54 
55```typescript
56const params = { uid: 1 }
57getUser(params)  // Query runs
58getUser(params)  // Cache hit (same reference)
59```
60 
61**Next.js-Specific Note:**
62 
63In Next.js, the `fetch` API is automatically extended with request memoization. Requests with the same URL and options are automatically deduplicated within a single request, so you don't need `React.cache()` for `fetch` calls. However, `React.cache()` is still essential for other async tasks:
64 
65- Database queries (Prisma, Drizzle, etc.)
66- Heavy computations
67- Authentication checks
68- File system operations
69- Any non-fetch async work
70 
71Use `React.cache()` to deduplicate these operations across your component tree.
72 
73Reference: [React.cache documentation](https://react.dev/reference/react/cache)
74