better-auth-effect

A Better Auth database adapter for @effect/sql.

Use any Effect SQL provider (PostgreSQL, MySQL, SQLite) with Better Auth.

Installation

npm install better-auth-effect
# or
pnpm add better-auth-effect

Peer Dependencies

npm install better-auth effect @effect/sql

And one of the database drivers:

# PostgreSQL
npm install @effect/sql-pg

# MySQL
npm install @effect/sql-mysql2

# SQLite
npm install @effect/sql-sqlite-node

Usage

Next.js App Router with Effect Layers

// lib/auth.ts
import { Effect, Layer } from "effect"
import { SqlClient } from "@effect/sql"
import { PgClient } from "@effect/sql-pg"
import { HttpApp } from "@effect/platform"
import { effectSqlAdapter } from "better-auth-effect"
import { betterAuth } from "better-auth"

const DatabaseLive = PgClient.layer({
  url: "postgresql://postgres:password@localhost:5432/myapp",
})

const AuthLive = Layer.scoped(Auth, Effect.gen(function* () {
  const rt = yield* Effect.runtime<SqlClient.SqlClient>()
  return betterAuth({
    database: effectSqlAdapter({ runtime: rt, dialect: "pg" }),
  })
})).pipe(Layer.provide(DatabaseLive))

const AuthAppLayer = Layer.mergeAll(AuthLive, DatabaseLive)

const { handler } = HttpApp.toWebHandlerLayer(authHttpApp, AuthAppLayer)

// app/api/auth/[...all]/route.ts
export const GET = (request: Request) => handler(request)
export const POST = (request: Request) => handler(request)

Configuration

interface EffectSqlAdapterConfig {
  /**
   * Runtime that provides SqlClient.
   * Obtain via Effect.runtime<SqlClient>() inside a Layer,
   * or from await ManagedRuntime.make(layer).runtime().
   */
  runtime: Runtime.Runtime<SqlClient>

  /**
   * Database dialect for SQL differences (RETURNING clause, etc.)
   * - "pg": PostgreSQL
   * - "mysql": MySQL
   * - "sqlite": SQLite
   */
  dialect: "pg" | "mysql" | "sqlite"

  /**
   * Enable debug logging for adapter operations.
   * @default false
   */
  debugLogs?: boolean
}

Why Runtime?

The adapter accepts an Effect Runtime — a lightweight handle that carries the environment (connection pool, services) needed to run effects. By obtaining the Runtime inside a Layer, you naturally share the same connection pool between Better Auth and your Effect application code without managing lifecycle manually.

Database Support

| Database | Dialect | RETURNING Support | |------------|------------|-------------------| | PostgreSQL | "pg" | Native | | SQLite | "sqlite" | Native (3.35+) | | MySQL | "mysql" | Emulated* |

* MySQL doesn't support RETURNING. The adapter uses LAST_INSERT_ID() + SELECT as a fallback. Tables must have an id column as primary key. This is not a problem for Better Auth, which always uses id.

Column Naming (snake_case / camelCase)

Better Auth uses camelCase field names (emailVerified, accessToken). If your database uses snake_case columns (email_verified, access_token), configure transformation in PgClient.layer:

import { PgClient } from "@effect/sql-pg"

const snakeToCamel = (str: string) =>
  str.replace(/_([a-z])/g, (_, letter) => letter.toUpperCase())

const camelToSnake = (str: string) =>
  str.replace(/[A-Z]/g, (letter) => `_${letter.toLowerCase()}`)

const SqlLive = PgClient.layer({
  database: "myapp",
  // Transform column names automatically
  transformResultNames: snakeToCamel,  // DB → JS (snake_case → camelCase)
  transformQueryNames: camelToSnake,   // JS → DB (camelCase → snake_case)
})

This is configured once at the client level and applies to all queries automatically.

Supported Operations

All Better Auth adapter methods are implemented:

• create - Insert with RETURNING
• findOne - SELECT with WHERE, LIMIT 1
• findMany - SELECT with WHERE, ORDER BY, LIMIT, OFFSET
• update - UPDATE with RETURNING
• updateMany - UPDATE multiple rows
• delete - DELETE single row
• deleteMany - DELETE multiple rows
• count - SELECT COUNT(*)

Error Handling

The adapter maps SQL errors to typed errors:

import {
  AdapterError,
  ConstraintViolationError,
  ConnectionError
} from "better-auth-effect"

• ConstraintViolationError - Unique/foreign key violations
• ConnectionError - Database connection issues
• AdapterError - Other SQL errors

License

MIT