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Architecture Overview

This document describes the high-level architecture of the Circle Backend.

System Design

The application follows a Monolithic Architecture using a layered structure. It is built to be modular within a single codebase, allowing for straightforward development and deployment while maintaining clear separation of concerns.

Layers

  1. Presentation Layer (Routes & Controllers)

    • Routes: Define the API endpoints and map them to specific controller functions.
    • Controllers: Handle incoming HTTP requests, validate input (using Zod), and return HTTP responses. They delegate business logic to the Service layer.

  2. Business Logic Layer (Services)

    • Services: Contain the core business rules and logic. They interact with the Data Access Layer and perform operations like user authentication, thread creation, and calculations.

  3. Data Access Layer (Prisma ORM)

    • Prisma Client: Provides a type-safe interface to the PostgreSQL database.
    • Models: Defined in schema.prisma.

  4. Caching Layer (Redis)

    • Used for caching frequently accessed data (e.g., feed, user profiles) to reduce database load and improve response times.

  5. External Services

    • Cloudinary: For storing and optimizing user-uploaded images (avatars, cover photos, thread images).

Request Flow

The following Mermaid diagram illustrates the flow of a typical request (e.g., creating a thread):

sequenceDiagram
    participant Client
    participant Router
    participant Controller
    participant Service
    participant Database
    participant Redis
    participant Cloudinary

    Client->>Router: POST /api/v1/threads
    Router->>Controller: createThread(req, res)
    Controller->>Service: createThread(data, file)
    
    alt Has Image
        Service->>Cloudinary: Upload Image
        Cloudinary-->>Service: Image URL
    end

    Service->>Database: Prisma.thread.create()
    Database-->>Service: Created Thread
    
    Service->>Redis: Invalidate Feed Cache
    Redis-->>Service: OK
    
    Service-->>Controller: Return Thread Object
    Controller-->>Client: 201 Created (JSON)
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Directory Structure

Key directories in src/:

  • v1/: Contains version 1 API resources.
    • Uses a feature-based or resource-based grouping (implied to be checked further, but standard practice).
  • config/: Configuration files (Redis connection, Cloudinary setup).
  • prisma/: Database schema and migrations.
  • swagger/: API documentation configuration.

Key Technologies

  • Express.js: Web app framework.
  • Prisma: Next-generation ORM for Node.js and TypeScript.
  • Redis: In-memory data structures store, used as database, cache, and message broker.
  • Zod: TypeScript-first schema declaration and validation library.