codexmachina
registry/nextjs-mysql-clerk-fitness

Fitness tracker on Next.js 16 (App Router), MySQL 8 and Clerk

verified 2026-07-15next16.2.9mysql23.22.6postgres3.4.9@clerk/nextjs7.5.15@neondatabase/serverless1.1.0

Type-checked against the real SDKs, migration applied to a live MySQL 8, 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
MySQL 8pooled

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).

MySQL 8

MySQL 8 via Drizzle ORM and the mysql2 driver.

Clerk

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

Fitness tracker

Fitness tracker — user-owned workout plans, a shared exercise catalog, append-only workout logs, and per-set reps/weight rows.

Setup

bun add next react react-dom drizzle-orm mysql2 @clerk/nextjs
DATABASE_URLMySQL connection string (mysql://…)
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/mysql2";
import mysql from "mysql2/promise";

// ponytail: single module-level pool; the runtime + mysql2's pool handle concurrency,
// so no globalThis singleton dance needed.
const pool = mysql.createPool(process.env.DATABASE_URL!);

export const db = drizzle({ client: pool });

// 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>
  );
}

Fitness tracker schema: plans, exercises, logs & sets

Workout plans

user-owned training plans that group and label a series of workout sessions

Exercise catalog

shared, user-agnostic library of exercises keyed by unique name and optional muscle group

Workout logs & sets

append-only workout log rows with child log_sets recording per-set reps and weight

src/db/schema.ts
// === file: src/db/schema.ts ===
import { relations } from "drizzle-orm";
import {
  decimal,
  index,
  int,
  mysqlTable,
  text,
  timestamp,
  varchar,
} from "drizzle-orm/mysql-core";
// Better Auth owns identity; we only reference its `user` table by id.
import { user } from "./auth-schema";

export const workoutPlans = mysqlTable(
  "workout_plans",
  {
    id: varchar("id", { length: 36 }).primaryKey(),
    ownerId: varchar("owner_id", { length: 255 }).notNull().references(() => user.id, { onDelete: "cascade" }),
    name: text("name").notNull(),
    createdAt: timestamp("created_at").notNull().defaultNow(),
  },
  (t) => [index("idx_plan_owner").on(t.ownerId)],
);

// Shared catalog, not user-owned.
export const exercises = mysqlTable("exercises", {
  id: varchar("id", { length: 36 }).primaryKey(),
  name: varchar("name", { length: 255 }).notNull().unique(),
  muscleGroup: text("muscle_group"),
});

export const workoutLogs = mysqlTable(
  "workout_logs",
  {
    id: varchar("id", { length: 36 }).primaryKey(),
    userId: varchar("user_id", { length: 255 }).notNull().references(() => user.id, { onDelete: "cascade" }),
    planId: varchar("plan_id", { length: 36 }).references(() => workoutPlans.id, { onDelete: "set null" }),
    performedAt: timestamp("performed_at").notNull(),
  },
  (t) => [index("idx_log_user_time").on(t.userId, t.performedAt)],
);

export const logSets = mysqlTable(
  "log_sets",
  {
    id: varchar("id", { length: 36 }).primaryKey(),
    logId: varchar("log_id", { length: 36 }).notNull().references(() => workoutLogs.id, { onDelete: "cascade" }),
    exerciseId: varchar("exercise_id", { length: 36 }).notNull().references(() => exercises.id),
    setNumber: int("set_number").notNull(),
    reps: int("reps").notNull(),
    weightKg: decimal("weight_kg", { precision: 20, scale: 6 }),
  },
  (t) => [index("idx_set_log").on(t.logId)],
);

export const workoutPlansRelations = relations(workoutPlans, ({ one, many }) => ({
  owner: one(user, { fields: [workoutPlans.ownerId], references: [user.id] }),
  logs: many(workoutLogs),
}));
export const workoutLogsRelations = relations(workoutLogs, ({ one, many }) => ({
  user: one(user, { fields: [workoutLogs.userId], references: [user.id] }),
  plan: one(workoutPlans, { fields: [workoutLogs.planId], references: [workoutPlans.id] }),
  sets: many(logSets),
}));
export const logSetsRelations = relations(logSets, ({ one }) => ({
  log: one(workoutLogs, { fields: [logSets.logId], references: [workoutLogs.id] }),
  exercise: one(exercises, { fields: [logSets.exerciseId], references: [exercises.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 { mysqlTable, text, timestamp, varchar } from "drizzle-orm/mysql-core";

// Local mirror of Clerk identity — the FK target app-type schemas reference as user.
// id = Clerk's user id (varchar(255), matching the app-type user_id FKs), so existing
// user_id foreign keys resolve once the sync runs. This IS the auth-schema slot for Clerk cells.
export const user = mysqlTable("user", {
  id: varchar("id", { length: 255 }).primaryKey(), // = Clerk user id
  email: text("email"),
  firstName: text("first_name"),
  lastName: text("last_name"),
  imageUrl: text("image_url"),
  updatedAt: timestamp("updated_at"), // staleness key (Clerk updated_at)
  createdAt: timestamp("created_at").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 (MySQL).
// Keyed on id (= Clerk id, the PK); the staleness guard lives in the UPDATE WHERE. MySQL has no
// RETURNING — affectedRows tells us what happened. The insert path catches the unique-key race (a
// concurrent delivery of the same NEW user) as an idempotent no-op, rethrowing every other error.
// 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));
    return { changed: deleted[0].affectedRows > 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))));
  if (updated[0].affectedRows > 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 };

  // The row doesn't exist yet — insert it. A concurrent delivery of the SAME new user can win the
  // race between our SELECT and this INSERT; the PK then rejects ours (ER_DUP_ENTRY) — an idempotent
  // no-op, NOT a change. Any other error is real: rethrow so the webhook fails loud and Clerk retries.
  try {
    await db.insert(user).values({ id: d.id, ...fields });
    return { changed: true };
  } catch (err: any) {
    if ((err?.cause?.code ?? err?.code) === "ER_DUP_ENTRY") return { changed: false };
    throw err;
  }
}
// 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/mysql2";
import mysql from "mysql2/promise";

// Serverless: a small pool per short-lived instance — many instances × a big pool exhausts MySQL.
export const pool = mysql.createPool({ uri: process.env.DATABASE_URL!, connectionLimit: 2 });
export const db = drizzle({ client: pool });

import { drizzle } from "drizzle-orm/mysql2";
import mysql from "mysql2/promise";

// Long-running process: a real, reused pool (mysql2 manages idle recycling).
export const pool = mysql.createPool({ uri: process.env.DATABASE_URL!, connectionLimit: 10 });
export const db = drizzle({ client: pool });

import { drizzle } from "drizzle-orm/planetscale-serverless";
import { Client } from "@planetscale/database";

// Edge/Workers have NO TCP sockets, so mysql2 cannot run here. PlanetScale's HTTP driver
// speaks MySQL over fetch — the client that works on Workers (the MySQL analog of Neon's HTTP driver).
const client = new Client({ url: process.env.DATABASE_URL! });
export const db = drizzle({ client });

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

mysql2's pool multiplexes connections; drizzle-orm/mysql2 wraps it. One module-level pool is right for a serverless/edge app — the runtime and the pool handle concurrency.

note

MySQL has no row-level security: multi-tenant isolation is enforced in application code via the forOrg helper (src/lib/tenant.ts), not by the database. See the tenant-scoping section on SaaS pages.

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

exercises.name carries a unique constraint — the exercise catalog is shared across all users, so duplicate names are a schema error, not a soft collision.

note

workout_logs.plan_id is set null on plan deletion, not cascaded — historical logs are preserved even when the originating plan is removed.

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.

caveat

MySQL provides no row-level security. On MySQL, multi-tenant isolation is APP-ENFORCED via the forOrg helper (src/lib/tenant.ts), not database-enforced like Postgres RLS. Every org-scoped query MUST go through forOrg — a missed query leaks across tenants. Postgres cells enforce this in the database itself (RLS), so it holds even for a query that forgets to scope.