Bkend Cookbook

bkend-cookbook

bkend.ai practical project tutorials and troubleshooting guide

1. Projects Overview

Choosing a Project

• First time with bkend? Start with Blog -- minimal tables, straightforward CRUD.
• Want cross-platform? Pick Recipe App -- covers both web and mobile patterns.
• Need transactional logic? Go with Shopping Mall -- order state machine and payment flow.
• Building a mobile-first app? Try Social Network -- Flutter-native with feed algorithms.

2. Blog Project

Level: Beginner | Tables: 3 | Frontend: Next.js | Time: ~2 hours

2.1 Schema Design (3 Tables)

users

posts

comments

2.2 Quick Start (5 Minutes)

Step 1: Create the Project

Use the bkend Console or MCP tool to create a new project named my-blog.

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> Create a new project called "my-blog"

Step 2: Create Tables

Create the three tables with the schemas defined above.

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> Create a "users" table with columns: name (string, required), email (string, required), avatar (string)
> Create a "posts" table with columns: title (string, required), content (string, required), authorId (string, required), status (string, required), tags (array)
> Create a "comments" table with columns: content (string, required), postId (string, required), authorId (string, required)

Step 3: Test the API

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# Create a user
curl -X POST https://api-client.bkend.ai/v1/data/users \
  -H "Content-Type: application/json" \
  -H "X-Project-Id: <your-project-id>" \
  -H "X-Environment: dev" \
  -H "X-API-Key: <your-api-key>" \
  -d '{"name": "Alice", "email": "alice@example.com"}'

# Create a post
curl -X POST https://api-client.bkend.ai/v1/data/posts \
  -H "Content-Type: application/json" \
  -H "X-Project-Id: <your-project-id>" \
  -H "X-Environment: dev" \
  -H "X-API-Key: <your-api-key>" \
  -d '{"title": "Hello World", "content": "My first post!", "authorId": "<user-id>", "status": "published", "tags": ["intro"]}'

# List all published posts
curl "https://api-client.bkend.ai/v1/data/posts?filter=%7B%22status%22%3A%22published%22%7D" \
  -H "X-Project-Id: <your-project-id>" \
  -H "X-Environment: dev" \
  -H "X-API-Key: <your-api-key>"

2.3 AI Prompt Collection

Use these prompts with Gemini CLI or Claude Code to accelerate development:

Schema & Data:

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> Create a blog schema with users, posts, and comments tables
> Add 5 sample blog posts with different tags and statuses
> Query all published posts sorted by newest first
> Find posts tagged with "tutorial" by author Alice

Frontend:

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> Generate a Next.js blog layout with header, sidebar, and post list
> Create a Markdown editor component for writing blog posts
> Build a comment section with nested replies
> Add tag filtering to the blog post list page

API Integration:

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> Create a bkendFetch wrapper for the blog API
> Build TanStack Query hooks for posts CRUD operations
> Add optimistic update for the comment submission form
> Implement infinite scroll pagination for the post feed

3. Recipe App Project

Level: Intermediate | Tables: 5 | Frontend: Next.js + Flutter | Time: ~4 hours

3.1 Schema Design (5 Tables)

users

recipes

ingredients

categories

favorites

3.2 Architecture

Web (Next.js):

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Stack: Next.js App Router + TanStack Query + Zustand

• Next.js App Router -- file-based routing with server components
• TanStack Query -- server state management, caching, and background refetching
• Zustand -- lightweight client state (UI state, filters, modals)

Mobile (Flutter):

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Stack: Flutter + Dio + Riverpod

• Flutter -- cross-platform UI framework
• Dio -- HTTP client with interceptor support
• Riverpod -- state management with dependency injection

3.3 AI Prompt Collection

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> Create the recipe app schema with users, recipes, ingredients, categories, and favorites
> Build a recipe card grid component with image, title, and cook time
> Implement category-based filtering with a sidebar navigation
> Create a favorites toggle button with optimistic update
> Generate a Flutter recipe detail screen with ingredient checklist

4. Shopping Mall Project

Level: Intermediate | Tables: 4 | Frontend: Next.js | Time: ~5 hours

4.1 Schema Design (4 Tables)

users

products

orders

order_items

4.2 Order State Machine

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                          +--> cancelled
                          |
draft --> pending --> paid --> shipped --> delivered --> completed
                     |                       |
                     +--> cancelled           +--> cancelled

State Transitions:

Implementation Pattern:

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// application/services/order-state-machine.ts

type OrderStatus =
  | "draft"
  | "pending"
  | "paid"
  | "shipped"
  | "delivered"
  | "completed"
  | "cancelled";

const VALID_TRANSITIONS: Record<OrderStatus, OrderStatus[]> = {
  draft: ["pending"],
  pending: ["paid", "cancelled"],
  paid: ["shipped", "cancelled"],
  shipped: ["delivered"],
  delivered: ["completed", "cancelled"],
  completed: [],
  cancelled: [],
};

export function canTransition(
  currentStatus: OrderStatus,
  nextStatus: OrderStatus
): boolean {
  return VALID_TRANSITIONS[currentStatus]?.includes(nextStatus) ?? false;
}

export async function transitionOrder(
  orderId: string,
  nextStatus: OrderStatus
): Promise<void> {
  const order = await bkendFetch(`/v1/data/orders/${orderId}`);
  const current = order.data.status as OrderStatus;

  if (!canTransition(current, nextStatus)) {
    throw new Error(
      `Invalid transition: ${current} -> ${nextStatus}`
    );
  }

  const updates: Record<string, any> = { status: nextStatus };

  if (nextStatus === "paid") updates.paidAt = new Date().toISOString();
  if (nextStatus === "shipped") updates.shippedAt = new Date().toISOString();
  if (nextStatus === "delivered") updates.deliveredAt = new Date().toISOString();

  await bkendFetch(`/v1/data/orders/${orderId}`, {
    method: "PUT",
    body: JSON.stringify(updates),
  });
}

4.3 AI Prompt Collection

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> Create the shopping mall schema with users, products, orders, and order_items tables
> Build a product catalog page with grid view, filters, and sorting
> Implement a shopping cart with Zustand state management
> Create an order checkout flow with address form and payment step
> Build an admin dashboard for order management with status transitions
> Add stock validation before order submission

5. Social Network Project

Level: Beginner | Tables: 5 | Frontend: Flutter | Time: ~3 hours

5.1 Schema Design (5 Tables)

users

posts

comments

likes

follows

5.2 Feed Algorithm Pattern

The social feed displays posts from users that the current user follows, sorted by newest first.

Step 1: Get the list of users the current user follows

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GET /v1/data/follows?filter={"followerId":"<current-user-id>"}&limit=100

Step 2: Extract the followingIds

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const followingIds = followsData.data.map(
  (f: { followingId: string }) => f.followingId
);

Step 3: Query posts from followed users

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GET /v1/data/posts?filter={"authorId":{"$in":[...followingIds]}}&sort={"createdAt":-1}&limit=20

Complete Feed Implementation (Flutter + Riverpod):

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// lib/features/feed/providers/feed_provider.dart

final feedProvider = FutureProvider.autoDispose<List<Post>>((ref) async {
  final currentUserId = ref.read(authProvider).userId;
  final client = ref.read(bkendClientProvider);

  // Step 1: Get following list
  final followsRes = await client.get('/v1/data/follows', queryParameters: {
    'filter': '{"followerId":"$currentUserId"}',
    'limit': '100',
  });

  final followingIds = (followsRes.data['data'] as List)
      .map((f) => f['followingId'] as String)
      .toList();

  if (followingIds.isEmpty) return [];

  // Step 2: Get posts from followed users
  final idsJson = followingIds.map((id) => '"$id"').join(',');
  final postsRes = await client.get('/v1/data/posts', queryParameters: {
    'filter': '{"authorId":{"\$in":[$idsJson]}}',
    'sort': '{"createdAt":-1}',
    'limit': '20',
  });

  return (postsRes.data['data'] as List)
      .map((json) => Post.fromJson(json))
      .toList();
});

5.3 Counter Cache Pattern

Counter caches denormalize counts for performance. When a user likes a post, update both the likes table and the likesCount on the post.

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Future<void> toggleLike(String postId, String userId, bool isLiked) async {
  if (isLiked) {
    // Unlike: remove like record and decrement counter
    final likesRes = await client.get('/v1/data/likes', queryParameters: {
      'filter': '{"postId":"$postId","userId":"$userId"}',
    });
    final likeId = likesRes.data['data'][0]['_id'];
    await client.delete('/v1/data/likes/$likeId');

    // Decrement counter
    final post = await client.get('/v1/data/posts/$postId');
    final currentCount = post.data['data']['likesCount'] ?? 0;
    await client.put('/v1/data/posts/$postId', data: {
      'likesCount': currentCount - 1,
    });
  } else {
    // Like: create like record and increment counter
    await client.post('/v1/data/likes', data: {
      'postId': postId,
      'userId': userId,
    });

    final post = await client.get('/v1/data/posts/$postId');
    final currentCount = post.data['data']['likesCount'] ?? 0;
    await client.put('/v1/data/posts/$postId', data: {
      'likesCount': currentCount + 1,
    });
  }
}

5.4 AI Prompt Collection

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> Create the social network schema with users, posts, comments, likes, and follows tables
> Build a Flutter feed screen with pull-to-refresh and infinite scroll
> Implement a like button with optimistic update and counter cache
> Create a user profile screen with follower/following counts
> Build a follow/unfollow toggle with real-time count update
> Generate a comment bottom sheet with auto-focus text input

6. Common Architecture Patterns

6.1 Next.js App Structure

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app/
  (app)/                    # Authenticated layout group
    dashboard/
      page.tsx
    posts/
      page.tsx
      [id]/
        page.tsx
    settings/
      page.tsx
    layout.tsx              # App shell with sidebar + header
  (auth)/                   # Auth layout group
    login/
      page.tsx
    signup/
      page.tsx
    layout.tsx              # Minimal auth layout
  api/                      # API routes (if needed)
    webhooks/
      route.ts
  layout.tsx                # Root layout
  page.tsx                  # Landing page

application/
  dto/                      # Data Transfer Objects
    post.dto.ts
    user.dto.ts
    order.dto.ts
  hooks/
    queries/                # TanStack Query hooks
      use-posts.ts
      use-users.ts
      use-orders.ts
    mutations/              # TanStack Mutation hooks
      use-create-post.ts
      use-update-order.ts
  services/                 # Business logic
    order-state-machine.ts

infrastructure/
  api/
    client.ts               # bkendFetch wrapper
    endpoints.ts             # API endpoint constants
  auth/
    middleware.ts            # Auth middleware
    session.ts               # Session helpers

components/
  ui/                        # Radix UI primitives
  shared/                    # Shared components
  features/                  # Feature-specific components

6.2 Flutter App Structure

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lib/
  core/
    network/
      bkend_client.dart      # Dio client setup
      auth_interceptor.dart   # Token refresh interceptor
      endpoints.dart          # API endpoint constants
    constants/
      app_constants.dart
    theme/
      app_theme.dart
    utils/
      validators.dart

  features/
    auth/
      data/
        auth_repository.dart
      models/
        user_model.dart
      presentation/
        login_screen.dart
        signup_screen.dart
      providers/
        auth_provider.dart

    feed/
      data/
        feed_repository.dart
      models/
        post_model.dart
      presentation/
        feed_screen.dart
        post_card.dart
      providers/
        feed_provider.dart

    profile/
      data/
        profile_repository.dart
      models/
        profile_model.dart
      presentation/
        profile_screen.dart
      providers/
        profile_provider.dart

  shared/
    widgets/
      loading_indicator.dart
      error_widget.dart
      empty_state.dart
    extensions/
      string_extensions.dart
      date_extensions.dart

  app.dart                    # MaterialApp with router
  main.dart                   # Entry point

7. Key Implementation Patterns

Pattern 1: bkendFetch Wrapper

Centralized API client that handles headers, auth tokens, and error formatting.

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// infrastructure/api/client.ts
export async function bkendFetch<T = any>(
  path: string,
  options: BkendFetchOptions = {}
): Promise<{ success: boolean; data: T; meta?: any }> {
  const { token, headers: customHeaders, ...rest } = options;
  const headers: Record<string, string> = {
    "Content-Type": "application/json",
    "X-Project-Id": process.env.NEXT_PUBLIC_BKEND_PROJECT_ID!,
    "X-Environment": process.env.NEXT_PUBLIC_BKEND_ENVIRONMENT!,
    ...customHeaders as Record<string, string>,
  };
  if (typeof window === "undefined" && process.env.BKEND_API_KEY) {
    headers["X-API-Key"] = process.env.BKEND_API_KEY;
  }
  if (token) {
    headers["Authorization"] = `Bearer ${token}`;
  }
  const res = await fetch(
    `${process.env.NEXT_PUBLIC_BKEND_API_URL}${path}`,
    { headers, ...rest }
  );
  if (!res.ok) {
    const error = await res.json();
    throw new Error(error.error?.message || "bkend API error");
  }
  return res.json();
}

Pattern 2: Mock Mode Toggle

Switch between real API and mock data for offline development.

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// infrastructure/api/client.ts
const USE_MOCK = process.env.NEXT_PUBLIC_USE_MOCK === "true";

export async function bkendFetch<T>(path: string, options?: BkendFetchOptions): Promise<T> {
  if (USE_MOCK) {
    const { getMockData } = await import("@/mocks/handlers");
    return getMockData<T>(path, options);
  }
  // ... real fetch implementation
}

Pattern 3: DTO Layer

Transform API responses into typed application objects.

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// application/dto/post.dto.ts
export interface PostDTO {
  _id: string;
  title: string;
  content: string;
  authorId: string;
  status: "draft" | "published";
  tags: string[];
  createdAt: string;
  updatedAt: string;
}

export interface CreatePostDTO {
  title: string;
  content: string;
  authorId: string;
  status: "draft" | "published";
  tags?: string[];
}

export function toPost(dto: PostDTO): Post {
  return {
    id: dto._id,
    title: dto.title,
    content: dto.content,
    authorId: dto.authorId,
    status: dto.status,
    tags: dto.tags ?? [],
    createdAt: new Date(dto.createdAt),
    updatedAt: new Date(dto.updatedAt),
  };
}

Pattern 4: Query Key Factory

Organized query keys for TanStack Query cache management.

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// application/hooks/queries/query-keys.ts
export const postKeys = {
  all: ["posts"] as const,
  lists: () => [...postKeys.all, "list"] as const,
  list: (filters: PostFilters) => [...postKeys.lists(), filters] as const,
  details: () => [...postKeys.all, "detail"] as const,
  detail: (id: string) => [...postKeys.details(), id] as const,
};

// Usage:
// queryClient.invalidateQueries({ queryKey: postKeys.lists() });

Pattern 5: Counter Cache

Maintain denormalized counts to avoid expensive aggregate queries.

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// When creating a comment, also update the post's commentsCount
await bkendFetch("/v1/data/comments", {
  method: "POST",
  body: JSON.stringify({ content, postId, authorId }),
});

const post = await bkendFetch(`/v1/data/posts/${postId}`);
await bkendFetch(`/v1/data/posts/${postId}`, {
  method: "PUT",
  body: JSON.stringify({
    commentsCount: (post.data.commentsCount ?? 0) + 1,
  }),
});

Pattern 6: Order State Machine

See Section 4.2 for the full order state machine implementation.

Pattern 7: Optimistic Updates

Update the UI before the server confirms, then rollback on error.

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// application/hooks/mutations/use-toggle-like.ts
export function useToggleLike(postId: string) {
  const queryClient = useQueryClient();
  return useMutation({
    mutationFn: (isLiked: boolean) => toggleLikeAPI(postId, isLiked),
    onMutate: async (isLiked) => {
      await queryClient.cancelQueries({ queryKey: postKeys.detail(postId) });
      const previous = queryClient.getQueryData(postKeys.detail(postId));
      queryClient.setQueryData(postKeys.detail(postId), (old: any) => ({
        ...old,
        likesCount: old.likesCount + (isLiked ? -1 : 1),
        isLiked: !isLiked,
      }));
      return { previous };
    },
    onError: (_err, _vars, context) => {
      queryClient.setQueryData(postKeys.detail(postId), context?.previous);
    },
    onSettled: () => {
      queryClient.invalidateQueries({ queryKey: postKeys.detail(postId) });
    },
  });
}

Pattern 8: Image Upload with Preview

Upload images to bkend storage with client-side preview.

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export function useImageUpload() {
  const [preview, setPreview] = useState<string | null>(null);

  const handleUpload = async (file: File): Promise<string> => {
    // Client-side preview
    const reader = new FileReader();
    reader.onload = (e) => setPreview(e.target?.result as string);
    reader.readAsDataURL(file);

    // Upload to bkend storage
    const formData = new FormData();
    formData.append("file", file);
    const res = await fetch(
      `${process.env.NEXT_PUBLIC_BKEND_API_URL}/v1/storage/upload`,
      {
        method: "POST",
        headers: {
          "X-Project-Id": process.env.NEXT_PUBLIC_BKEND_PROJECT_ID!,
          "X-Environment": process.env.NEXT_PUBLIC_BKEND_ENVIRONMENT!,
        },
        body: formData,
      }
    );
    const data = await res.json();
    return data.data.url;
  };

  return { preview, handleUpload };
}

Pattern 9: Infinite Scroll Pagination

Cursor-based pagination for feeds and lists.

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// application/hooks/queries/use-posts-infinite.ts
export function usePostsInfinite(filters?: PostFilters) {
  return useInfiniteQuery({
    queryKey: postKeys.list(filters ?? {}),
    queryFn: async ({ pageParam }) => {
      const params = new URLSearchParams();
      params.set("limit", "20");
      if (pageParam) params.set("cursor", pageParam);
      if (filters?.status) {
        params.set("filter", JSON.stringify({ status: filters.status }));
      }
      params.set("sort", JSON.stringify({ createdAt: -1 }));

      return bkendFetch<PostsResponse>(
        `/v1/data/posts?${params.toString()}`
      );
    },
    initialPageParam: undefined as string | undefined,
    getNextPageParam: (lastPage) => lastPage.meta?.nextCursor ?? undefined,
  });
}

Pattern 10: Real-time Subscription (Planned)

Note: Real-time subscriptions are planned for a future bkend.ai release.

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// Planned API (not yet available)
// const unsubscribe = bkend.subscribe("posts", {
//   filter: { status: "published" },
//   onInsert: (post) => queryClient.invalidateQueries(postKeys.lists()),
//   onUpdate: (post) => queryClient.invalidateQueries(postKeys.detail(post._id)),
//   onDelete: (id) => queryClient.invalidateQueries(postKeys.lists()),
// });

Pattern 11: Auth Middleware

See the bkend-quickstart skill for the full Next.js middleware implementation. Key points:

• Check for bkend_access_token cookie
• Auto-refresh using bkend_refresh_token when access token expires
• Redirect to /login for unauthenticated requests
• Skip auth for public routes

Pattern 12: Error Boundary

Catch and display errors gracefully at the component level.

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// components/shared/error-boundary.tsx
"use client";
import { useQueryErrorResetBoundary } from "@tanstack/react-query";
import { ErrorBoundary as ReactErrorBoundary } from "react-error-boundary";

export function QueryErrorBoundary({ children }: { children: React.ReactNode }) {
  const { reset } = useQueryErrorResetBoundary();
  return (
    <ReactErrorBoundary
      onReset={reset}
      fallbackRender={({ error, resetErrorBoundary }) => (
        <div className="flex flex-col items-center gap-4 p-8">
          <p className="text-red-500">Something went wrong: {error.message}</p>
          <button onClick={resetErrorBoundary} className="btn btn-primary">
            Try Again
          </button>
        </div>
      )}
    >
      {children}
    </ReactErrorBoundary>
  );
}

Pattern 13: Loading Skeleton

Display placeholder UI while data is loading.

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// components/shared/post-skeleton.tsx
export function PostSkeleton() {
  return (
    <div className="animate-pulse space-y-3 p-4 border rounded-lg">
      <div className="flex items-center gap-3">
        <div className="w-10 h-10 bg-gray-200 rounded-full" />
        <div className="h-4 bg-gray-200 rounded w-24" />
      </div>
      <div className="h-4 bg-gray-200 rounded w-full" />
      <div className="h-4 bg-gray-200 rounded w-3/4" />
      <div className="h-32 bg-gray-200 rounded w-full" />
    </div>
  );
}

Pattern 14: Form Validation (Zod)

Schema-based validation for forms.

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// application/dto/post.dto.ts
import { z } from "zod";

export const createPostSchema = z.object({
  title: z.string().min(1, "Title is required").max(200, "Title too long"),
  content: z.string().min(1, "Content is required"),
  status: z.enum(["draft", "published"]),
  tags: z.array(z.string()).max(10, "Maximum 10 tags").optional(),
});

export type CreatePostInput = z.infer<typeof createPostSchema>;

// Usage with react-hook-form:
// const form = useForm<CreatePostInput>({
//   resolver: zodResolver(createPostSchema),
// });

Pattern 15: Search Debounce

Debounce search input to reduce API calls.

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// application/hooks/use-debounced-search.ts
import { useState, useEffect } from "react";

export function useDebouncedSearch(delay = 300) {
  const [searchTerm, setSearchTerm] = useState("");
  const [debouncedTerm, setDebouncedTerm] = useState("");

  useEffect(() => {
    const timer = setTimeout(() => setDebouncedTerm(searchTerm), delay);
    return () => clearTimeout(timer);
  }, [searchTerm, delay]);

  return { searchTerm, setSearchTerm, debouncedTerm };
}

// Usage:
// const { searchTerm, setSearchTerm, debouncedTerm } = useDebouncedSearch();
// const { data } = useQuery({
//   queryKey: ["posts", "search", debouncedTerm],
//   queryFn: () => bkendFetch(`/v1/data/posts?filter={"title":{"$regex":"${debouncedTerm}"}}`),
//   enabled: debouncedTerm.length > 0,
// });

8. Dependencies

Next.js Projects

Flutter Projects

9. Quick Reference

API Endpoints Used Across Projects

Query Parameters

Next Steps

After completing a cookbook project, consider these skills for deeper topics: