docs: improve "Dedupe Middleware" (#260)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **Refactor**
- Streamlined backend middleware to optimize database connection reuse
and reduce redundant initialization.
- Enhanced authentication handling by refining session management for
more reliable user validation.

Overall, these updates improve backend efficiency and stability to
deliver a smoother, more consistent application experience.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: unnoq

apps/content/docs/best-practices/dedupe-middleware.md

@@ -28,11 +28,12 @@ declare function connectDb(): Promise<'a_fake_db'>
 const dbProvider = os
   .$context<{ db?: Awaited<ReturnType<typeof connectDb>> }>()
   .middleware(async ({ context, next }) => {
-    if (context.db) {
-      return next({ context: { db: context.db } })
-    }
+    /**
+     * If db already exists, skip the connection.
+     */
+    const db = context.db ?? await connectDb() // [!code highlight]
 
-    return next({ context: { db: await connectDb() } })
+    return next({ context: { db } })
   })
 ```
 
@@ -45,22 +46,27 @@ declare function connectDb(): Promise<'a_fake_db'>
 const dbProvider = os
   .$context<{ db?: Awaited<ReturnType<typeof connectDb>> }>()
   .middleware(async ({ context, next }) => {
-    if (context.db) {
-      return next({ context: { db: context.db } })
-    }
-    const db = await connectDb()
+    const db = context.db ?? await connectDb()
+
     return next({ context: { db } })
   })
 // ---cut---
 const foo = os.use(dbProvider).handler(({ context }) => 'Hello World')
 
 const bar = os.use(dbProvider).handler(({ context }) => {
-  const result = call(foo, 'input', { context })
+  /**
+   * Now when you call foo, the dbProvider middleware no need to connect to the database again.
+   */
+  const result = call(foo, 'input', { context }) // [!code highlight]
+
   return 'Hello World'
 })
 
+/**
+ * Now even when `dbProvider` is applied multiple times, it still only connects to the database once.
+ */
 const router = os
-  .use(dbProvider)
+  .use(dbProvider) // [!code highlight]
   .use(({ next }) => {
     // Additional middleware logic
     return next()

playgrounds/contract-first/src/middlewares/db.ts

@@ -18,15 +18,12 @@ export interface DB {
 export const dbProviderMiddleware = os
   .$context<{ db?: DB }>()
   .middleware(async ({ context, next }) => {
-    if (context.db) {
-      return next({
-        context: {
-          db: context.db,
-        },
-      })
-    }
-
-    const db: DB = createFakeDB()
+    /**
+     * Why we should ?? here?
+     * Because it can avoid `createFakeDB` being called when unnecessary.
+     * {@link https://orpc.unnoq.com/docs/best-practices/dedupe-middleware}
+     */
+    const db: DB = context.db ?? createFakeDB()
 
     return next({
       context: {

playgrounds/nextjs/src/middlewares/auth.ts

@@ -1,32 +1,35 @@
 import type { User } from '@/schemas/user'
 import { os } from '@orpc/server'
 
-/**
- * Best practices for dedupe-middlewares
- * {@link https://orpc.unnoq.com/docs/best-practices/dedupe-middleware}
- */
 export const requiredAuthMiddleware = os
-  .$context<{ user?: User }>()
-  .middleware(({ context, next }) => {
-    if (context.user) {
-      return next({
-        context: { user: context.user },
-      })
-    }
-
+  .$context<{ session?: { user?: User } }>()
+  .middleware(async ({ context, next }) => {
     /**
-     * You can use headers or cookies here to create the user object:
-     * import { cookies, headers } from 'next/headers'
-     * const headerList = await headers();
-     * const cookieList = await cookies();
-     *
-     * These lines are commented out because Stackblitz has issues with Next.js headers and cookies.
-     * However, this works fine in a local environment.
+     * Why we should ?? here?
+     * Because it can avoid `getSession` being called when unnecessary.
+     * {@link https://orpc.unnoq.com/docs/best-practices/dedupe-middleware}
      */
+    const session = context.session ?? await getSession()
 
-    const user: User = { id: 'unique', name: 'unnoq', email: '[email protected]' }
+    if (!session.user) {
+      throw new Error('UNAUTHORIZED')
+    }
 
     return next({
-      context: { user },
+      context: { user: session.user },
     })
   })
+
+async function getSession() {
+  /**
+   * You can use headers or cookies here to create the user object:
+   * import { cookies, headers } from 'next/headers'
+   * const headerList = await headers();
+   * const cookieList = await cookies();
+   *
+   * These lines are commented out because Stackblitz has issues with Next.js headers and cookies.
+   * However, this works fine in a local environment.
+   */
+
+  return { user: { id: 'unique', name: 'unnoq', email: '[email protected]' } }
+}

playgrounds/nextjs/src/middlewares/db.ts

@@ -11,22 +11,15 @@ export interface DB {
   }
 }
 
-/**
- * Best practices for dedupe-middlewares
- * {@link https://orpc.unnoq.com/docs/best-practices/dedupe-middleware}
- */
 export const dbProviderMiddleware = os
   .$context<{ db?: DB }>()
   .middleware(async ({ context, next }) => {
-    if (context.db) {
-      return next({
-        context: {
-          db: context.db,
-        },
-      })
-    }
-
-    const db: DB = createFakeDB()
+    /**
+     * Why we should ?? here?
+     * Because it can avoid `createFakeDB` being called when unnecessary.
+     * {@link https://orpc.unnoq.com/docs/best-practices/dedupe-middleware}
+     */
+    const db: DB = context.db ?? createFakeDB()
 
     return next({
       context: {

playgrounds/nuxt/server/middlewares/db.ts

@@ -11,22 +11,15 @@ export interface DB {
   }
 }
 
-/**
- * Best practices for dedupe-middlewares
- * {@link https://orpc.unnoq.com/docs/best-practices/dedupe-middleware}
- */
 export const dbProviderMiddleware = os
   .$context<{ db?: DB }>()
   .middleware(async ({ context, next }) => {
-    if (context.db) {
-      return next({
-        context: {
-          db: context.db,
-        },
-      })
-    }
-
-    const db: DB = createFakeDB()
+    /**
+     * Why we should ?? here?
+     * Because it can avoid `createFakeDB` being called when unnecessary.
+     * {@link https://orpc.unnoq.com/docs/best-practices/dedupe-middleware}
+     */
+    const db: DB = context.db ?? createFakeDB()
 
     return next({
       context: {

playgrounds/solid-start/src/middlewares/db.ts

@@ -11,22 +11,15 @@ export interface DB {
   }
 }
 
-/**
- * Best practices for dedupe-middlewares
- * {@link https://orpc.unnoq.com/docs/best-practices/dedupe-middleware}
- */
 export const dbProviderMiddleware = os
   .$context<{ db?: DB }>()
   .middleware(async ({ context, next }) => {
-    if (context.db) {
-      return next({
-        context: {
-          db: context.db,
-        },
-      })
-    }
-
-    const db: DB = createFakeDB()
+    /**
+     * Why we should ?? here?
+     * Because it can avoid `createFakeDB` being called when unnecessary.
+     * {@link https://orpc.unnoq.com/docs/best-practices/dedupe-middleware}
+     */
+    const db: DB = context.db ?? createFakeDB()
 
     return next({
       context: {

playgrounds/svelte-kit/src/middlewares/db.ts

@@ -11,22 +11,15 @@ export interface DB {
   }
 }
 
-/**
- * Best practices for dedupe-middlewares
- * {@link https://orpc.unnoq.com/docs/best-practices/dedupe-middleware}
- */
 export const dbProviderMiddleware = os
   .$context<{ db?: DB }>()
   .middleware(async ({ context, next }) => {
-    if (context.db) {
-      return next({
-        context: {
-          db: context.db,
-        },
-      })
-    }
-
-    const db: DB = createFakeDB()
+    /**
+     * Why we should ?? here?
+     * Because it can avoid `createFakeDB` being called when unnecessary.
+     * {@link https://orpc.unnoq.com/docs/best-practices/dedupe-middleware}
+     */
+    const db: DB = context.db ?? createFakeDB()
 
     return next({
       context: {