Bug description

When using two separate Prisma clients with different database adapters (PostgreSQL via @prisma/adapter-pg and MySQL via @prisma/adapter-mariadb) in the same Node.js process, the second client call fails with a deserialization error suggesting the rust-free client is incorrectly reusing state from the first client's adapter type.

Both clients use the new rust-free client configuration (engineType = "client"). The first query to the PostgreSQL client works fine, but any subsequent query to the MySQL client fails with:

Error: unknown variant `mysql`, expected `postgres`

This suggests there's shared state or deserialization logic that doesn't properly handle multiple adapter types in the same process.

Severity

🚨 Critical: Data loss, app crash, security issue

Reproduction

Step 1: Generate Two Prisma Clients

PostgreSQL Schema (prisma/postgres/schema.prisma):

generator client {
  provider     = "prisma-client"
  output       = "../../generated/postgres-client"
  engineType   = "client"
  moduleFormat = "cjs"
  runtime      = "nodejs"
}

datasource db {
  provider = "postgresql"
  url      = env("POSTGRES_DATABASE_URL")
}

model User {
  id    Int    @id @default(autoincrement())
  email String @unique
  name  String
}

MySQL Schema (prisma/mysql/schema.prisma):

generator client {
  provider     = "prisma-client"
  output       = "../../generated/mysql-client"
  engineType   = "client"
  moduleFormat = "cjs"
  runtime      = "nodejs"
}

datasource db {
  provider = "mysql"
  url      = env("MYSQL_DATABASE_URL")
}

model User {
  id    Int    @id @default(autoincrement())
  email String @unique
  name  String
}

Run npx prisma generate for both schemas.

Step 2: Initialize Both Clients with Adapters

File: database.ts

import { PrismaClient as PostgresClient } from "./generated/postgres-client";
import { PrismaClient as MySQLClient } from "./generated/mysql-client";
import { PrismaPg } from "@prisma/adapter-pg";
import { PrismaMariaDb } from "@prisma/adapter-mariadb";
import { Pool } from "pg";

// PostgreSQL client
const postgresClient = new PostgresClient({
    adapter: new PrismaPg(
        new Pool({
            connectionString: process.env.POSTGRES_DATABASE_URL,
        }),
        {
            schema: "public",
        },
    ),
});

// MySQL client
const mysqlUrl = new URL(process.env.MYSQL_DATABASE_URL);
const mysqlClient = new MySQLClient({
    adapter: new PrismaMariaDb({
        host: mysqlUrl.hostname,
        user: mysqlUrl.username,
        password: mysqlUrl.password,
        database: mysqlUrl.pathname.slice(1),
        port: Number(mysqlUrl.port),
    }),
});

export { postgresClient, mysqlClient };

Step 3: Execute Queries on Both Clients

File: reproduce-issue.ts

import { postgresClient, mysqlClient } from "./database";

async function main() {
    // First query to PostgreSQL - works fine
    const postgresData = await postgresClient.user.findFirst();
    console.log("PostgreSQL query succeeded:", postgresData);

    // Second query to MySQL - fails with error
    const mysqlData = await mysqlClient.user.findFirst();
    console.log("MySQL query succeeded:", mysqlData);
}

main().catch(console.error);

Step 4: Run the Script

node reproduce-issue.ts

Expected vs. Actual Behavior

Expected Behavior

Both Prisma clients should work independently in the same process. The PostgreSQL query should execute successfully, followed by the MySQL query executing successfully, allowing applications to query multiple databases with different providers.

Expected output:

PostgreSQL query succeeded: { id: 1, email: 'user@example.com', name: 'John' }
MySQL query succeeded: { id: 1, email: 'admin@example.com', name: 'Admin' }

Actual Behavior

The first query to PostgreSQL succeeds, but the second query to MySQL fails with a deserialization error:

PostgreSQL query succeeded: { id: 1, email: 'user@example.com', name: 'John' }
Error: unknown variant `mysql`, expected `postgres`

The error suggests that the rust-free client's internal state is incorrectly using the PostgreSQL adapter's type when attempting to deserialize or process the MySQL client's operations.

Frequency

Consistently reproducible

Does this occur in development or production?

Both development and production

Is this a regression?

Unknown - this is the first time attempting to use multiple Prisma clients with different adapters in the same process with the rust-free client. This configuration may not have been tested or supported in previous versions.

Workaround

Reveting to the rust client

Prisma Schema & Queries

PostgreSQL Schema (prisma/postgres/schema.prisma)

generator client {
  provider     = "prisma-client"
  output       = "../../generated/postgres-client"
  engineType   = "client"
  moduleFormat = "cjs"
  runtime      = "nodejs"
}

datasource db {
  provider = "postgresql"
  url      = env("POSTGRES_DATABASE_URL")
}

model User {
  id    Int    @id @default(autoincrement())
  email String @unique
  name  String
}

MySQL Schema (prisma/mysql/schema.prisma)

generator client {
  provider     = "prisma-client"
  output       = "../../generated/mysql-client"
  engineType   = "client"
  moduleFormat = "cjs"
  runtime      = "nodejs"
}

datasource db {
  provider = "mysql"
  url      = env("MYSQL_DATABASE_URL")
}

model User {
  id    Int    @id @default(autoincrement())
  email String @unique
  name  String
}

Queries

// PostgreSQL query - succeeds
await postgresClient.user.findFirst();

// MySQL query - fails
await mysqlClient.user.findFirst();

Prisma Config

Both schemas use identical generator configuration:

generator client {
  provider     = "prisma-client"
  output       = "[different output paths]"
  engineType   = "client"      // Rust-free client
  moduleFormat = "cjs"
  runtime      = "nodejs"
}

Key configuration details:

• engineType = "client" - Using the new rust-free client (WASM-based)
• moduleFormat = "cjs" - CommonJS module format
• runtime = "nodejs" - Node.js runtime
• Separate output directories for each client

Logs & Debug Info

Error Message

Error: unknown variant `mysql`, expected `postgres`

Environment & Setup

• OS: Linux (WSL2)
• Node.js version: v22.10.0

Prisma Version

prisma                  : 6.16.3
@prisma/client          : 6.16.3
@prisma/adapter-pg      : 6.16.3
@prisma/adapter-mariadb : 6.16.3