Next.js 16 SaaS Database Schema with Prisma: Users, Subscriptions, and AI Chat

If you're building a SaaS app with Next.js 16, one of the most important decisions you'll make early on is your database schema. Get it right and everything from billing to AI features slots in cleanly. Get it wrong and you'll be writing migrations for months. In this guide, I'll walk you through a production-ready Prisma schema that covers users, subscriptions, and AI chat history — the core entities in virtually every modern SaaS. Prerequisites Next.js 16 app (App Router) Prisma 5+ PostgreSQL (local or Supabase/Neon) Node.js 20+ Why Prisma for SaaS? Prisma gives you: Type-safe queries — no raw SQL foot-guns Auto-generated migrations — schema-first workflow Excellent Next.js integration — works great with React Server Components and API routes Prisma Studio — a visual DB editor you'll actually use Step 1: Install and Initialize Prisma npm install prisma @prisma/client npx prisma init --datasource-provider postgresql This creates a prisma/schema.prisma file and a .env with a DATABASE_U