Architecture & DevOps8 min readAvnish Yadav

Why Clean Architecture Wins in Next.js 15: Structuring Domain Logic & Server Actions

Stop dumping SQL queries directly inside React Server Components. Here is how Clean Architecture isolates domain rules, decouples databases, and makes your Next.js 15 app 100% testable.

Featured typescript Implementation

// domain/use-cases/checkout.ts — Zero framework dependency!
export interface OrderRepository {
  createOrder(userId: string, itemSlug: string, amountCents: number): Promise<{ id: string; licenseKey: string }>;
}

export class ProcessCheckoutUseCase {
  constructor(private orderRepo: OrderRepository, private paymentGateway: PaymentGateway) {}

  async execute(input: { userId: string; itemSlug: string; priceCents: number }) {
    if (input.priceCents < 0) throw new Error("Invalid price");
    const payment = await this.paymentGateway.charge(input.priceCents);
    return await this.orderRepo.createOrder(input.userId, input.itemSlug, input.priceCents);
  }
}

The Server Component Trap in Next.js 15

When React Server Components (RSC) and Server Actions were introduced, thousands of tutorials advocated querying the database directly inside `page.tsx`. While acceptable for prototypes, this creates tight coupling that cripples growing production systems.

When your business logic is intertwined with UI rendering code, you cannot unit test authorization logic without mocking React, and migrating from SQLite/Turso to Postgres requires rewriting entire page trees.

The Three Layers of Clean Architecture in Next.js

1. **Domain Layer (`/core/domain`)**: Contains entities, value objects, and business rules. Zero dependencies on Next.js, React, or Drizzle. 2. **Application / Use Cases (`/core/use-cases`)**: Coordinates execution flows like checkout, license key issuance, and password resets. 3. **Infrastructure / Adapters (`/infra`)**: Implements interfaces using concrete libraries (Turso libSQL, Stripe SDK, Resend, Cloudflare R2).

Benefits Realized in Production - 100% Deterministic Testing: Run 50 unit tests in under 200ms using in-memory mock repositories without spinning up a test database. - Framework Portability: Your core business use cases can run seamlessly inside Next.js Server Actions, background cron scripts, or standalone CLI utilities. - Zero Accidental Leaks: Sensitive secrets and raw database transactions are strictly isolated from client-rendered React components.

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Why Clean Architecture Wins in Next.js 15: Structuring Domain Logic & Server Actions

The Server Component Trap in Next.js 15

The Three Layers of Clean Architecture in Next.js

Free Download: Next.js 15 Clean Architecture Folder Structure Cheat Sheet

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