Better Auth’s tables, as real Mongoose models.

The problem

Most Node backends already running MongoDB use Mongoose, not the raw driver. It’s close to universal in NestJS and Express apps. Better Auth talking straight to mongodb instead isn’t just a style mismatch. It produces four specific problems, and they’ve been open on Better Auth’s own GitHub since February 2025.

1. 01

   An extra dependency you didn't ask for.

   Even a Mongoose-only project ends up with the raw mongodb package installed, just for Better Auth's own tables.

   better-auth #1492

2. 02

   Two connections, no shared schema.

   Better Auth writes user, session, and account documents straight through MongoClient. Your own Mongoose models never see those writes: no validation, no hooks, no virtuals.

3. 03

   populate() breaks.

   Reference a Better-Auth-created document from your own schema, and .populate() silently fails, alongside _id type mismatches between Better Auth's ID handling and Mongoose's ObjectId.

   better-auth #6289discussion #9364

4. 04

   The only fix on offer is a workaround.

   Every answer in Better Auth's own discussions comes down to reaching into mongoose.connection.getClient() and handing the raw client over. That sidesteps the schema and populate problems instead of solving them.

   discussion #1921

The documented workaround, versus this

Both connect to the same database. Only one of them gives your own code a real, extensible model to work with afterward.

import { betterAuth } from "better-auth";
import { mongodbAdapter } from "better-auth/adapters/mongodb";
import mongoose from "mongoose";

await mongoose.connect(process.env.MONGO_URI!);

export const auth = betterAuth({
  // Reach into Mongoose's own connection to hand Better Auth a raw
  // client. No schema, no validation, no hooks — and now two ways
  // to read the same collections.
  database: mongodbAdapter(mongoose.connection.getClient().db()),
});

import { betterAuth } from "better-auth";
import { mongooseAdapter } from "better-auth-mongoose";
import mongoose from "mongoose";

await mongoose.connect(process.env.MONGO_URI!);

export const auth = betterAuth({
  database: mongooseAdapter(mongoose.connection),
});

Proof, not claims

This isn’t marketing copy. It’s a real, CI-run test in the repo.

const auth = betterAuth({ database: mongooseAdapter(connection) });

const { user } = await auth.api.signUpEmail({
  body: {
    email: "author@example.com",
    password: "correct-horse-battery-staple",
    name: "Post Author",
  },
});

// A consumer-defined model, with a real ObjectId ref to Better
// Auth's own "user" collection.
const Post = connection.model(
  "Post",
  new Schema({
    title: String,
    author: { type: Schema.Types.ObjectId, ref: "user", required: true },
  }),
);

await Post.create({ title: "Hello, populate()", author: coerceToObjectId(user.id) });

const post = await Post.findOne({ title: "Hello, populate()" })
  .populate("author")
  .lean()
  .exec();

post.author.email; // "author@example.com" — resolved by plain Mongoose .populate()

Two packages

The adapter stands on its own. The tenant plugin is optional, and only useful if you’re already using Better Auth’s organization plugin.

better-auth-mongoose

The adapter. Start here.

Real, extensible Mongoose models for Better Auth's own tables. .populate(), schema validation, and hooks all work normally from your own application code.

pnpm add better-auth-mongoose mongoose better-authCopy

npmREADME

better-auth-mongoose-tenant

Optional. Automatic tenant isolation.

Tenant-scoped query middleware on top of Better Auth's organization plugin. Every read and write on the models you name gets scoped to the active organization, with no .where() to forget.

pnpm add better-auth-mongoose-tenantCopy

npmREADME

Recipes

Every snippet here is lifted straight from the packages’ own READMEs and tests, not written for this page.

import { betterAuth } from "better-auth";
import { mongooseAdapter } from "better-auth-mongoose";
import mongoose from "mongoose";

await mongoose.connect(process.env.MONGO_URI!);

export const auth = betterAuth({
  database: mongooseAdapter(mongoose.connection),
  emailAndPassword: { enabled: true },
});

Compatibility

Peer ranges, and where CI actually exercises them. Nothing here is a claim without a workflow run behind it.

Frequently asked