Marketplace on Next.js 16 (App Router) + Postgres (Neon) + Better Auth

✓ Verified 2026-06-21 · next 16.2.9 · postgres 3.4.9 · better-auth 1.6.20

Type-checked against the real SDKs, migration applied to a live Postgres, pooling tested — then tracked for upstream drift and re-verified when it moves. How we verify →

What you're getting

Setup

bun add next react react-dom drizzle-orm postgres better-auth

Environment variables:

Apply the schema: bunx drizzle-kit push

Initialization

src/lib/db.ts — Database client

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 });

src/lib/auth.ts — Auth instance

// Better Auth instance (self-hosted, Next.js 16 (App Router)).
import { betterAuth } from "better-auth";
import { drizzleAdapter } from "better-auth/adapters/drizzle";
// Reuse the SAME postgres-js/Drizzle client the db slice exported in
// src/lib/db.ts — Better Auth shares the pooled `DATABASE_URL` connection.
import { db } from "./db";

export const auth = betterAuth({
  // Drizzle adapter over the shared client; provider "pg" => Postgres DDL
  // for Better Auth's own user/session/account/verification tables.
  database: drizzleAdapter(db, { provider: "pg" }),
  // ponytail: email+password is the shortest real auth that works out of
  // the box — add socialProviders / plugins here when the app needs them.
  emailAndPassword: { enabled: true },
  secret: process.env.BETTER_AUTH_SECRET,
  baseURL: process.env.BETTER_AUTH_URL,
});

export type Session = typeof auth.$Infer.Session;

app/api/auth/[...all]/route.ts — Route handler

// Mount Better Auth on Next's route layer.
import { toNextJsHandler } from "better-auth/next-js";
import { auth } from "@/lib/auth";

export const { GET, POST } = toNextJsHandler(auth);

proxy.ts — Route protection

// Session-protection proxy for Next.js 16 (App Router) (Next 16 renamed middleware.ts → proxy.ts).
// ponytail: getSessionCookie only checks the cookie EXISTS (no DB hit at
// the Edge runtime) — do the real auth.api.getSession() check inside
// protected Server Components / route handlers. This just bounces
// logged-out users before render.
import { NextResponse, type NextRequest } from "next/server";
import { getSessionCookie } from "better-auth/cookies";

export function proxy(request: NextRequest) {
  const sessionCookie = getSessionCookie(request);
  if (!sessionCookie) {
    return NextResponse.redirect(new URL("/sign-in", request.url));
  }
  return NextResponse.next();
}

export const config = {
  // ponytail: guard the SaaS app surface; widen the matcher per app-type.
  matcher: ["/dashboard/:path*", "/settings/:path*"],
};

Two-sided marketplace schema: sellers, listings, orders, payouts & reviews

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

export type SellerStatus = "pending" | "active" | "suspended";
export type ListingStatus = "draft" | "active" | "sold" | "archived";
export type OrderStatus =
  | "pending"
  | "paid"
  | "shipped"
  | "completed"
  | "refunded"
  | "canceled";
export type PayoutStatus = "scheduled" | "processing" | "paid" | "failed";

/** Supply side: a user who sells. One seller profile per user. */
export const sellers = pgTable(
  "sellers",
  {
    id: uuid("id").primaryKey().defaultRandom(),
    // Better Auth's user.id is text — match it, don't recast.
    userId: text("user_id")
      .notNull()
      .references(() => user.id, { onDelete: "cascade" }),
    displayName: text("display_name").notNull(),
    // ponytail: opaque payout-provider account id (Stripe Connect / PayPal) —
    // no provider FK needed; nullable until onboarding completes.
    payoutAccountId: text("payout_account_id"),
    status: text("status")
      .$type<SellerStatus>()
      .notNull()
      .default("pending"),
    createdAt: timestamp("created_at", { withTimezone: true })
      .notNull()
      .defaultNow(),
  },
  (t) => [
    // One seller profile per identity.
    unique("sellers_user_unique").on(t.userId),
    index("idx_seller_status").on(t.status),
    check(
      "sellers_status_check",
      sql`${t.status} in ('pending','active','suspended')`,
    ),
  ],
);

/** Catalog: each listing belongs to a seller. priceCents keeps money integer. */
export const listings = pgTable(
  "listings",
  {
    id: uuid("id").primaryKey().defaultRandom(),
    sellerId: uuid("seller_id")
      .notNull()
      .references(() => sellers.id, { onDelete: "cascade" }),
    title: text("title").notNull(),
    description: text("description"),
    priceCents: integer("price_cents").notNull().default(0),
    status: text("status")
      .$type<ListingStatus>()
      .notNull()
      .default("draft"),
    createdAt: timestamp("created_at", { withTimezone: true })
      .notNull()
      .defaultNow(),
  },
  (t) => [
    // Browse a seller's catalog; filter the storefront by live listings.
    index("idx_listing_seller").on(t.sellerId),
    index("idx_listing_status").on(t.status),
    check(
      "listings_status_check",
      sql`${t.status} in ('draft','active','sold','archived')`,
    ),
  ],
);

/** Demand side: a buyer (Better Auth user) purchases a listing. */
export const marketplaceOrders = pgTable(
  "marketplace_orders",
  {
    id: uuid("id").primaryKey().defaultRandom(),
    // The buyer is a Better Auth user — text id, like sellers.userId.
    buyerId: text("buyer_id")
      .notNull()
      .references(() => user.id, { onDelete: "cascade" }),
    listingId: uuid("listing_id")
      .notNull()
      .references(() => listings.id),
    // Captured at purchase time — independent of later listing price edits.
    amountCents: integer("amount_cents").notNull(),
    status: text("status")
      .$type<OrderStatus>()
      .notNull()
      .default("pending"),
    createdAt: timestamp("created_at", { withTimezone: true })
      .notNull()
      .defaultNow(),
  },
  (t) => [
    // Buyer's order history; reconcile orders against a listing.
    index("idx_order_buyer").on(t.buyerId),
    index("idx_order_listing").on(t.listingId),
    check(
      "marketplace_orders_status_check",
      sql`${t.status} in ('pending','paid','shipped','completed','refunded','canceled')`,
    ),
  ],
);

/** Money out: a payout settles a seller's earnings for a period. */
export const payouts = pgTable(
  "payouts",
  {
    id: uuid("id").primaryKey().defaultRandom(),
    sellerId: uuid("seller_id")
      .notNull()
      .references(() => sellers.id, { onDelete: "cascade" }),
    // Net amount remitted to the seller (gross minus marketplace fee).
    amountCents: bigint("amount_cents", { mode: "number" }).notNull(),
    status: text("status")
      .$type<PayoutStatus>()
      .notNull()
      .default("scheduled"),
    // Settlement window this payout covers, e.g. "2026-06".
    period: text("period").notNull(),
    createdAt: timestamp("created_at", { withTimezone: true })
      .notNull()
      .defaultNow(),
  },
  (t) => [
    // One payout per seller per settlement window.
    unique("payouts_seller_period_unique").on(t.sellerId, t.period),
    index("idx_payout_seller").on(t.sellerId),
    index("idx_payout_status").on(t.status),
    check(
      "payouts_status_check",
      sql`${t.status} in ('scheduled','processing','paid','failed')`,
    ),
  ],
);

/** Trust signal: a reviewer (Better Auth user) rates a listing 1-5. */
export const reviews = pgTable(
  "reviews",
  {
    id: uuid("id").primaryKey().defaultRandom(),
    listingId: uuid("listing_id")
      .notNull()
      .references(() => listings.id, { onDelete: "cascade" }),
    // Reviewer is a Better Auth user — text id.
    reviewerId: text("reviewer_id")
      .notNull()
      .references(() => user.id, { onDelete: "cascade" }),
    rating: integer("rating").notNull(),
    body: text("body"),
    createdAt: timestamp("created_at", { withTimezone: true })
      .notNull()
      .defaultNow(),
  },
  (t) => [
    // One review per reviewer per listing.
    unique("reviews_listing_reviewer_unique").on(t.listingId, t.reviewerId),
    // Render a listing's reviews + aggregate its rating.
    index("idx_review_listing").on(t.listingId),
    check("reviews_rating_check", sql`${t.rating} between 1 and 5`),
  ],
);

export const sellersRelations = relations(sellers, ({ one, many }) => ({
  user: one(user, { fields: [sellers.userId], references: [user.id] }),
  listings: many(listings),
  payouts: many(payouts),
}));

export const listingsRelations = relations(listings, ({ one, many }) => ({
  seller: one(sellers, {
    fields: [listings.sellerId],
    references: [sellers.id],
  }),
  orders: many(marketplaceOrders),
  reviews: many(reviews),
}));

export const marketplaceOrdersRelations = relations(
  marketplaceOrders,
  ({ one }) => ({
    buyer: one(user, {
      fields: [marketplaceOrders.buyerId],
      references: [user.id],
    }),
    listing: one(listings, {
      fields: [marketplaceOrders.listingId],
      references: [listings.id],
    }),
  }),
);

export const payoutsRelations = relations(payouts, ({ one }) => ({
  seller: one(sellers, {
    fields: [payouts.sellerId],
    references: [sellers.id],
  }),
}));

export const reviewsRelations = relations(reviews, ({ one }) => ({
  listing: one(listings, {
    fields: [reviews.listingId],
    references: [listings.id],
  }),
  reviewer: one(user, {
    fields: [reviews.reviewerId],
    references: [user.id],
  }),
}));

Connection & security

## Next.js 16 ↔ Postgres pooling (Neon pooled endpoint, PgBouncer transaction mode)

Connect through Neon's **pooled** endpoint (`-pooler` host) via `DATABASE_URL`. Serverless
functions are short-lived and concurrent, so PgBouncer in **transaction mode** is what keeps
Postgres' connection ceiling from being blown.

### `prepare: false` is mandatory
Transaction-mode PgBouncer hands each transaction a different backend, so server-side prepared
statements (postgres-js' default) silently break across the pool. Disable them on the client:
`postgres(url, { prepare: false })`. This is also why **Drizzle, not Prisma**, is paired here —
Prisma's prepared-statement reliance is a blocked intersection on this endpoint.

### Connection reuse
- Construct the postgres-js client at **module scope** (`src/lib/db.ts`) so warm function
  instances reuse one socket instead of opening one per request.
- Cap the driver pool small — `max: 1` per instance. The shared pool lives in PgBouncer, not in
  your function; a large per-instance `max` just multiplies idle connections across instances.
- Keep `idle_timeout` ~20s and `connect_timeout` ~10s so frozen instances release backends fast.

### No session-level features
Transaction mode forbids anything that spans transactions on one backend: `LISTEN/NOTIFY`,
session-scoped `SET`, advisory-lock sessions, server-side cursors, and `WITH HOLD`. Need any of
those? Use Neon's **direct** (non-pooled) endpoint for that path only.

### Thresholds
- Drizzle/postgres-js: `prepare: false`, `max: 1`, `idle_timeout: 20`, `connect_timeout: 10`.
- Neon Free pooled budget is ~10k client connections; keep concurrency well under the project's
  `max_connections` (often 100–900 by plan) by leaning on PgBouncer, never on driver pooling.

Decisions & compatibility

Related stacks