ERP Abstractions in Next.js: Building Reusable Business Logic Layers

Introduction

Enterprise Resource Planning systems are, at their core, about one thing: abstraction. Every SAP module, every Oracle workflow, every Odoo view is the result of years of thinking about how to separate business rules from presentation, how to make a purchase order look the same whether it's printed, emailed, or displayed in a browser.

When I moved from implementing ERP systems to building web applications with Next.js, the muscle memory didn't disappear — it adapted.

The Core Parallel

In ERP development, you think in three layers:

1. Master Data — the canonical records (products, customers, accounts)
2. Transaction Layer — the events that mutate master data (invoices, receipts, journal entries)
3. Reporting Layer — read-optimized views over the above

In a Next.js App Router application, this maps almost directly:

1. Data Models / Types — TypeScript interfaces and Zod schemas in /lib/types
2. Server Actions / API Routes — mutations, form submissions, CRON jobs
3. React Server Components — read-only, data-fetch-at-render views

Reusable Business Logic with Server Actions

One of the cleanest patterns I've found is extracting business logic into pure functions that server actions call. This keeps your route.ts files thin and your logic testable.

// lib/invoice.ts
export async function createInvoice(data: InvoiceInput): Promise<Invoice> {
  const validated = InvoiceSchema.parse(data);
  const lineTotal = validated.lines.reduce((sum, l) => sum + l.qty * l.rate, 0);
  const tax = lineTotal * validated.taxRate;
  return db.invoice.create({ ...validated, lineTotal, tax, total: lineTotal + tax });
}

// app/api/invoices/route.ts
import { createInvoice } from "@/lib/invoice";

export async function POST(req: Request) {
  const body = await req.json();
  const invoice = await createInvoice(body);
  return Response.json(invoice, { status: 201 });
}

Shared State: The ERP Session Analogy

ERP systems maintain session context — the company code, the fiscal year, the user's role. In a multi-tenant Next.js application, you replicate this with a combination of middleware and React context.

Conclusion

The best software architecture, whether it's an S/4HANA customization or a React app, shares the same fundamental discipline: keep business rules in one place, and let the presentation layer be a thin consumer of them.

ERP thinking made me a better web developer. The patterns are older than the frameworks.