Client & Connections

Decision tree

Are you on Workers / Lambda / Edge / per-invocation runtime?
  YES → serverless: true  (factory)
  NO  → long-running Node server?
          YES → uri + await createClient (singleton)
          NO  → scripts/CLI → uri mode or MongoClient directly

Serverless mode

import { createClient, type SchemasToClient } from "mondel";
import { schemas } from "./schemas";

export type DbClient = SchemasToClient<typeof schemas>;

export const connect = createClient({
  serverless: true,
  schemas,
  validation: "strict",
});

// Later:
const db = await connect(env.MONGODB_URI, {
  // optional MongoClientOptions
  maxPoolSize: 5,
});
try {
  return await db.users.findMany({});
} finally {
  await db.close();
}

Client methods

Method	Description
db.<schemaName>	Collection proxy
db.close()	Close underlying MongoClient
db.getDb()	Native Db
db.startSession(options?)	Transactions

Node mode

const db = await createClient({
  uri: process.env.MONGODB_URI!,
  schemas,
  validation: "strict",
  options: {
    maxPoolSize: 20,
  },
});

// Reuse `db` for the process lifetime
// On shutdown:
await db.close();

Multiple databases

Use separate clients, not a named-connection map:

const main = await createClient({ uri: process.env.MAIN_URI!, schemas: appSchemas });
const analytics = await createClient({
  uri: process.env.ANALYTICS_URI!,
  schemas: eventSchemas,
});

Connection hygiene

Environment	Guidance
Express / Fastify	One client at startup; close on SIGTERM
Cloudflare Workers	Factory in module scope; connect in fetch; prefer Atlas + reasonable pool
AWS Lambda	Reuse client across invocations when the runtime freezes the isolate; avoid connect+close every time if the platform reuses the process
High concurrency serverless	Watch Atlas connection limits; consider smaller maxPoolSize, Private Link, or a proxy

Mondel does not implement its own pool — the official driver does. Pass MongoClientOptions through options (node) or the second argument of the serverless factory.

Deprecated: syncIndexes

// Avoid on the hot path
createClient({ syncIndexes: true, ... });

Use:

npx mondel push --uri "$MONGODB_URI" --schema ./dist/schemas.js

Typing the client

import type { SchemasToClient } from "mondel";

const schemas = [userSchema] as const;
type Db = SchemasToClient<typeof schemas>;
// Db["users"] has findOne, create, ...

Without as const, TypeScript widens schema names and you lose precise db.users typing.