Social network on Next.js 16 (App Router), MySQL 8 and Better Auth

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 });

import { boolean, mysqlTable, text, timestamp, varchar } from "drizzle-orm/mysql-core";

export const user = mysqlTable("user", {
  id: varchar("id", { length: 255 }).primaryKey(),
  name: text("name").notNull(),
  email: varchar("email", { length: 255 }).notNull().unique(),
  emailVerified: boolean("email_verified").notNull().default(false),
  image: text("image"),
  createdAt: timestamp("created_at").notNull().defaultNow(),
  updatedAt: timestamp("updated_at").notNull().defaultNow(),
});

export const session = mysqlTable("session", {
  id: varchar("id", { length: 255 }).primaryKey(),
  expiresAt: timestamp("expires_at").notNull(),
  token: varchar("token", { length: 255 }).notNull().unique(),
  createdAt: timestamp("created_at").notNull().defaultNow(),
  updatedAt: timestamp("updated_at").notNull(),
  ipAddress: text("ip_address"),
  userAgent: text("user_agent"),
  userId: varchar("user_id", { length: 255 })
    .notNull()
    .references(() => user.id, { onDelete: "cascade" }),
});

export const account = mysqlTable("account", {
  id: varchar("id", { length: 255 }).primaryKey(),
  accountId: text("account_id").notNull(),
  providerId: text("provider_id").notNull(),
  userId: varchar("user_id", { length: 255 })
    .notNull()
    .references(() => user.id, { onDelete: "cascade" }),
  accessToken: text("access_token"),
  refreshToken: text("refresh_token"),
  idToken: text("id_token"),
  accessTokenExpiresAt: timestamp("access_token_expires_at"),
  refreshTokenExpiresAt: timestamp("refresh_token_expires_at"),
  scope: text("scope"),
  password: text("password"),
  createdAt: timestamp("created_at").notNull().defaultNow(),
  updatedAt: timestamp("updated_at").notNull(),
});

export const verification = mysqlTable("verification", {
  id: varchar("id", { length: 255 }).primaryKey(),
  identifier: text("identifier").notNull(),
  value: text("value").notNull(),
  expiresAt: timestamp("expires_at").notNull(),
  createdAt: timestamp("created_at").notNull().defaultNow(),
  updatedAt: timestamp("updated_at").notNull().defaultNow(),
});

// 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";
import * as authSchema from "@/db/auth-schema";

export const auth = betterAuth({
  // Drizzle adapter over the shared client. The schema is passed HERE (not into
  // drizzle()) — it is the only consumer that needs it, so the db client stays
  // schema-less. ponytail: do NOT enable experimental.joins; it is the one option
  // that would make the adapter reach into db._.fullSchema.
  // ponytail: usePlural stays false (the default) — with it true Better Auth would
  // look for `sessions`/`accounts` and could bind to the analytics/ledger app-type tables.
  database: drizzleAdapter(db, { provider: "mysql", schema: authSchema }),
  // 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;

// 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);

// 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*"],
};

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

/** Public profile, one per Better Auth user. handle is the @-name in the URL. */
export const profiles = mysqlTable(
  "profiles",
  {
    id: varchar("id", { length: 36 }).primaryKey(),
    // Better Auth's user.id is varchar(255) on MySQL — match it, don't recast. One profile per user.
    userId: varchar("user_id", { length: 255 })
      .notNull()
      .unique()
      .references(() => user.id, { onDelete: "cascade" }),
    handle: varchar("handle", { length: 255 }).notNull().unique(),
    bio: text("bio"),
    avatarUrl: text("avatar_url"),
    createdAt: timestamp("created_at").notNull().defaultNow(),
  },
  (t) => [index("idx_profile_handle").on(t.handle)],
);

/** Directed follow edge: follower -> following. Both ends are Better Auth users. */
export const follows = mysqlTable(
  "follows",
  {
    // Better Auth's user.id is varchar(255) on MySQL — match it, don't recast.
    followerId: varchar("follower_id", { length: 255 })
      .notNull()
      .references(() => user.id, { onDelete: "cascade" }),
    followingId: varchar("following_id", { length: 255 })
      .notNull()
      .references(() => user.id, { onDelete: "cascade" }),
    createdAt: timestamp("created_at").notNull().defaultNow(),
  },
  (t) => [
    primaryKey({ columns: [t.followerId, t.followingId] }),
    // The edge is the identity — you can't follow the same user twice.
    unique("follows_follower_following_unique").on(
      t.followerId,
      t.followingId,
    ),
    // Drives the "who follows this user" (followers list) query.
    index("idx_follow_following").on(t.followingId),
  ],
);

/** Authored post in the feed. */
export const posts = mysqlTable(
  "posts",
  {
    id: varchar("id", { length: 36 }).primaryKey(),
    // Better Auth's user.id is varchar(255) on MySQL — match it, don't recast.
    authorId: varchar("author_id", { length: 255 })
      .notNull()
      .references(() => user.id, { onDelete: "cascade" }),
    body: text("body").notNull(),
    createdAt: timestamp("created_at").notNull().defaultNow(),
  },
  (t) => [
    // Drives the per-author profile timeline query.
    index("idx_post_author").on(t.authorId),
  ],
);

/** post <-> user like edge. The composite unique is the like identity. */
export const postLikes = mysqlTable(
  "post_likes",
  {
    postId: varchar("post_id", { length: 36 })
      .notNull()
      .references(() => posts.id, { onDelete: "cascade" }),
    // Better Auth's user.id is varchar(255) on MySQL — match it, don't recast.
    userId: varchar("user_id", { length: 255 })
      .notNull()
      .references(() => user.id, { onDelete: "cascade" }),
    createdAt: timestamp("created_at").notNull().defaultNow(),
  },
  (t) => [
    primaryKey({ columns: [t.postId, t.userId] }),
    // One like per user per post.
    unique("post_likes_post_user_unique").on(t.postId, t.userId),
    index("idx_post_likes_user").on(t.userId),
  ],
);

export const profilesRelations = relations(profiles, ({ one }) => ({
  user: one(user, { fields: [profiles.userId], references: [user.id] }),
}));

export const followsRelations = relations(follows, ({ one }) => ({
  follower: one(user, {
    fields: [follows.followerId],
    references: [user.id],
  }),
  following: one(user, {
    fields: [follows.followingId],
    references: [user.id],
  }),
}));

export const postsRelations = relations(posts, ({ one, many }) => ({
  author: one(user, { fields: [posts.authorId], references: [user.id] }),
  likes: many(postLikes),
}));

export const postLikesRelations = relations(postLikes, ({ one }) => ({
  post: one(posts, {
    fields: [postLikes.postId],
    references: [posts.id],
  }),
  user: one(user, { fields: [postLikes.userId], references: [user.id] }),
}));

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 });