Skip to content

Core Concepts

FastAPI Fullstack generates production-ready applications with a clean, layered architecture.

Architecture Overview

graph TB
    subgraph Frontend["Frontend (Next.js 15)"]
        UI[React Components]
        WS[WebSocket Client]
        Store[Zustand Stores]
    end

    subgraph Backend["Backend (FastAPI)"]
        API[API Routes]
        Services[Services Layer]
        Repos[Repositories]
        Agent[AI Agent]
    end

    subgraph Infrastructure
        DB[(PostgreSQL/MongoDB)]
        Redis[(Redis)]
        Queue[Celery/Taskiq]
    end

    UI --> API
    WS <--> Agent
    API --> Services
    Services --> Repos
    Services --> Agent
    Repos --> DB
    Services --> Redis
    Services --> Queue

Key Concepts

  • Architecture

    Repository + Service pattern, dependency injection, and layered design.

  • AI Agents

    PydanticAI, LangChain, LangGraph, CrewAI with WebSocket streaming.

  • Frontend

    Next.js 15, React 19, TypeScript, Tailwind CSS, and Zustand.

Design Principles

1. Separation of Concerns

Each layer has a single responsibility:

Layer Responsibility
Routes HTTP handling, validation, auth
Services Business logic, orchestration
Repositories Data access, queries

2. Dependency Injection

FastAPI's dependency injection system is used throughout:

Python
@router.get("/users/{user_id}")
async def get_user(
    user_id: int,
    service: UserService = Depends(get_user_service),
) -> UserResponse:
    return await service.get_user(user_id)

3. Type Safety

Full type annotations with Pydantic models:

Python
class UserCreate(BaseModel):
    email: EmailStr
    password: str

class UserResponse(BaseModel):
    id: int
    email: EmailStr
    created_at: datetime

Next Steps