codexmachina
registry/nextjs-postgres-clerk-ledger

Fintech ledger on Next.js 16 (App Router), Postgres (Neon) and Clerk

verified 2026-07-15next16.2.9postgres3.4.9@clerk/nextjs7.5.15@neondatabase/serverless1.1.0

Type-checked against the real SDKs, migration applied to a live Postgres (Neon), connection clients load-tested, then tracked for upstream drift and re-verified when it moves. How we verify

request path
Browserrequest
fetch
Next.js 16 (App Router)routing + proxy
verify
Clerksession
query
Postgres (Neon)pooled

session validation runs in server components and route handlers, not at the edge

What you're getting

Next.js 16 (App Router)

Next.js 16 App Router — file-based routing, server components, and the Edge proxy (Next 16's renamed middleware).

Postgres (Neon)

Postgres on Neon via Drizzle ORM and the postgres-js driver.

Clerk

Clerk — hosted identity (sign-in UI, sessions, user management) mounted via middleware + provider.

Fintech ledger

Double-entry fintech ledger — chart of accounts, immutable journal entries, and debit/credit lines with integer-cent amounts.

Setup

bun add next react react-dom drizzle-orm postgres @clerk/nextjs
DATABASE_URLNeon pooled (-pooler) connection string
NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY
CLERK_SECRET_KEY
CLERK_WEBHOOK_SECRETsvix secret that verifies Clerk webhook signatures

Apply the schema with bunx drizzle-kit push

Initialization

Database client

src/lib/db.ts
import { drizzle } from "drizzle-orm/postgres-js";
import postgres from "postgres";

// Neon pooled endpoint = PgBouncer transaction mode → prepared statements off.
// ponytail: single module-level client; the serverless runtime + PgBouncer do
// the pooling, so no custom pool/globalThis singleton dance needed.
const client = postgres(process.env.DATABASE_URL!, { prepare: false });

export const db = drizzle({ client });

// ponytail: Clerk is hosted — set NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY and
// CLERK_SECRET_KEY in the env. The publishable key is read client-side by
// <ClerkProvider>; the secret key is read server-side by clerkMiddleware().
// Both are picked up from the environment automatically — no wiring needed.
// Clerk proxy for Next.js 16 (App Router) (Next 16 renamed middleware.ts → proxy.ts; clerkMiddleware is still the helper).
import { clerkMiddleware, createRouteMatcher } from "@clerk/nextjs/server";

// ponytail: guard the SaaS app surface; widen the matcher per app-type.
const isProtectedRoute = createRouteMatcher([
  "/dashboard(.*)",
  "/settings(.*)",
]);

export default clerkMiddleware(async (auth, request) => {
  // auth.protect() bounces logged-out users to Clerk's hosted sign-in.
  if (isProtectedRoute(request)) {
    await auth.protect();
  }
});

export const config = {
  // Clerk's documented matcher: skip Next internals + static files unless
  // referenced in search params, and always run on API/tRPC routes.
  matcher: [
    "/((?!_next|[^?]*\\.(?:html?|css|js(?!on)|jpe?g|webp|png|gif|svg|ttf|woff2?|ico|csv|docx?|xlsx?|zip|webmanifest)).*)",
    "/(api|trpc)(.*)",
  ],
};
// Root layout — <ClerkProvider> is required for Next.js 16 (App Router).
import { ClerkProvider } from "@clerk/nextjs";
import type { ReactNode } from "react";

export default function RootLayout({ children }: { children: ReactNode }) {
  return (
    <ClerkProvider>
      <html lang="en">
        <body>{children}</body>
      </html>
    </ClerkProvider>
  );
}

Double-entry ledger schema: accounts, journal entries & lines

Chart of accounts

per-owner accounts typed to one of five standard categories (asset/liability/equity/revenue/expense)

Journal entries

immutable header rows tying a description and posted timestamp to a creator

Debit/credit lines & balances

the individual debit/credit lines linking each journal entry to an account with an integer-cent amount

src/db/schema.ts
// === file: src/db/schema.ts ===
import { relations, sql } from "drizzle-orm";
import {
  bigint,
  check,
  index,
  pgTable,
  text,
  timestamp,
  uuid,
} from "drizzle-orm/pg-core";
// Better Auth owns identity; we only reference its `user` table by id.
import { user } from "./auth-schema";

export const accounts = pgTable(
  "accounts",
  {
    id: uuid("id").primaryKey().defaultRandom(),
    ownerId: text("owner_id").notNull().references(() => user.id, { onDelete: "cascade" }),
    name: text("name").notNull(),
    type: text("type").notNull(),
    currency: text("currency").notNull().default("USD"),
    createdAt: timestamp("created_at", { withTimezone: true }).notNull().defaultNow(),
  },
  (t) => [
    index("idx_account_owner").on(t.ownerId),
    check("accounts_type_check", sql`${t.type} in ('asset','liability','equity','revenue','expense')`),
  ],
);

export const journalEntries = pgTable(
  "journal_entries",
  {
    id: uuid("id").primaryKey().defaultRandom(),
    creatorId: text("creator_id").notNull().references(() => user.id, { onDelete: "cascade" }),
    description: text("description").notNull(),
    postedAt: timestamp("posted_at", { withTimezone: true }).notNull().defaultNow(),
  },
  (t) => [index("idx_entry_posted").on(t.postedAt)],
);

// Double-entry: each entry has >= 2 lines; debits must equal credits (enforced in app).
export const journalLines = pgTable(
  "journal_lines",
  {
    id: uuid("id").primaryKey().defaultRandom(),
    entryId: uuid("entry_id").notNull().references(() => journalEntries.id, { onDelete: "cascade" }),
    accountId: uuid("account_id").notNull().references(() => accounts.id, { onDelete: "cascade" }),
    direction: text("direction").notNull(),
    amountCents: bigint("amount_cents", { mode: "number" }).notNull(),
  },
  (t) => [
    index("idx_line_account").on(t.accountId),
    index("idx_line_entry").on(t.entryId),
    check("journal_lines_direction_check", sql`${t.direction} in ('debit','credit')`),
  ],
);

export const accountsRelations = relations(accounts, ({ one, many }) => ({
  owner: one(user, { fields: [accounts.ownerId], references: [user.id] }),
  lines: many(journalLines),
}));
export const journalEntriesRelations = relations(journalEntries, ({ one, many }) => ({
  creator: one(user, { fields: [journalEntries.creatorId], references: [user.id] }),
  lines: many(journalLines),
}));
export const journalLinesRelations = relations(journalLines, ({ one }) => ({
  entry: one(journalEntries, { fields: [journalLines.entryId], references: [journalEntries.id] }),
  account: one(accounts, { fields: [journalLines.accountId], references: [accounts.id] }),
}));

Verified identity sync (Clerk)

✓ Clerk users sync into a local user table idempotently: duplicate, out-of-order, and concurrent webhooks converge to one correct row. Replayed against a live database.
src/db/auth-schema.ts
// === file: src/db/auth-schema.ts ===
import { pgTable, text, timestamp } from "drizzle-orm/pg-core";

// Local mirror of Clerk identity — the FK target app-type schemas reference as user.
// id = Clerk's user id, so existing user_id foreign keys resolve once the sync runs.
// This IS the auth-schema slot for Clerk cells: the SaaS schema's ./auth-schema FK
// target (src/db/auth-schema.ts) resolves here, same slot Better Auth's generated file fills.
export const user = pgTable("user", {
  id: text("id").primaryKey(), // = Clerk user id
  email: text("email"),
  firstName: text("first_name"),
  lastName: text("last_name"),
  imageUrl: text("image_url"),
  updatedAt: timestamp("updated_at", { withTimezone: true }), // staleness key (Clerk updated_at)
  createdAt: timestamp("created_at", { withTimezone: true }).notNull().defaultNow(),
});

import { and, eq, isNull, lt, or } from "drizzle-orm";
import { user } from "@/db/auth-schema";

export type ClerkUserEvent = {
  type: string;
  data: {
    id: string;
    email_addresses?: { email_address: string }[];
    first_name?: string | null;
    last_name?: string | null;
    image_url?: string | null;
    updated_at?: number;
  };
};

// Idempotent + concurrency-safe sync of a Clerk user into the local user table.
// Keyed on id (= Clerk id, the PK); the staleness guard lives in the UPDATE WHERE so
// a late/older event cannot clobber newer state. user.deleted removes the row.
export async function recordClerkEvent(
  // ponytail: loosely typed Drizzle client so the emitted core stays portable.
  db: any,
  event: ClerkUserEvent,
): Promise<{ changed: boolean }> {
  const d = event.data;
  if (event.type === "user.deleted") {
    const deleted = await db.delete(user).where(eq(user.id, d.id)).returning({ id: user.id });
    return { changed: deleted.length > 0 };
  }

  const email = d.email_addresses?.[0]?.email_address ?? null;
  const eventAt = new Date(d.updated_at ?? 0);
  const fields = {
    email,
    firstName: d.first_name ?? null,
    lastName: d.last_name ?? null,
    imageUrl: d.image_url ?? null,
    updatedAt: eventAt,
  };

  const updated = await db
    .update(user)
    .set(fields)
    .where(and(eq(user.id, d.id), or(isNull(user.updatedAt), lt(user.updatedAt, eventAt))))
    .returning({ id: user.id });
  if (updated.length > 0) return { changed: true };

  const [existing] = await db.select({ id: user.id }).from(user).where(eq(user.id, d.id)).limit(1);
  if (existing) return { changed: false };

  const inserted = await db
    .insert(user)
    .values({ id: d.id, ...fields })
    .onConflictDoNothing({ target: user.id })
    .returning({ id: user.id });
  return { changed: inserted.length > 0 };
}
// Clerk identity webhook for Next.js 16 (App Router). Clerk webhooks are svix — verify the
// signature, then hand the event to the idempotent recordClerkEvent.
import { Webhook } from "svix";
import { db } from "@/lib/db";
import { recordClerkEvent, type ClerkUserEvent } from "@/lib/identity/record";

const USER_EVENTS = new Set(["user.created", "user.updated", "user.deleted"]);

export async function POST(request: Request): Promise<Response> {
  const secret = process.env.CLERK_WEBHOOK_SECRET;
  if (!secret) return Response.json({ error: "Server misconfigured" }, { status: 500 });

  const raw = await request.text();
  const headers = Object.fromEntries(request.headers.entries());

  let event: ClerkUserEvent;
  try {
    event = new Webhook(secret).verify(raw, headers) as ClerkUserEvent;
  } catch {
    return Response.json({ error: "Invalid signature" }, { status: 403 });
  }

  if (USER_EVENTS.has(event.type)) await recordClerkEvent(db, event);
  return Response.json({ ok: true });
}

Deploy targets

✓ The right DB client for where you deploy: load-tested with concurrent queries against a live database. Edge needs the HTTP driver (no TCP); serverless needs a tiny pool.
src/lib/db.ts
import { drizzle } from "drizzle-orm/postgres-js";
import postgres from "postgres";

// Serverless: one connection per (short-lived) instance; Neon's pooler multiplexes.
export const sql = postgres(process.env.DATABASE_URL!, { prepare: false, max: 1 });
export const db = drizzle(sql);

import { drizzle } from "drizzle-orm/postgres-js";
import postgres from "postgres";

// Long-running process: a real, reused pool. Still prepare:false on the pooled endpoint.
export const sql = postgres(process.env.DATABASE_URL!, { prepare: false, max: 10, idle_timeout: 20 });
export const db = drizzle(sql);

import { neon } from "@neondatabase/serverless";
import { drizzle } from "drizzle-orm/neon-http";

// Edge/Workers have NO TCP sockets, so postgres-js cannot run here. Neon's HTTP
// driver speaks Postgres over fetch — the only client that works on Workers.
export const sql = neon(process.env.DATABASE_URL!);
export const db = drizzle(sql);

Decisions and compatibility

note

Auth runs in proxy.ts (Next 16's renamed middleware) on the Edge runtime: it gates on the session cookie's presence only — full session validation happens in Server Components and route handlers, not in the proxy.

note

prepare: false is mandatory — Neon's pooled endpoint is PgBouncer in transaction mode, where server-side prepared statements break across the pool.

note

Drizzle is paired here (not Prisma): Prisma's prepared-statement reliance is incompatible with transaction-mode pooling.

note

Hosted: Clerk owns identity and does NOT create a local `user` table. Store `clerk_user_id` as text without a foreign key, or sync Clerk users into a local table via webhook before relying on FKs to `user`.

note

The accounts table constrains type to the five canonical categories (asset/liability/equity/revenue/expense) via a DB CHECK — adding a new account class requires a migration, not just app code.

note

Debit/credit balance (sum of debits == sum of credits per entry) is enforced in application logic, not at the DB level; the schema's CHECK only guards direction values ('debit'/'credit'), so the invariant can be violated if bypassed.

caveat

Clerk is a hosted identity provider and does not create a local `user` table. This schema's foreign keys to `user` assume a local identity table (as Better Auth provides). With Clerk, store `clerk_user_id` as a text column without a foreign key, or sync Clerk users into a local `users` table via webhook before relying on these FKs.