bubbles-express-generator/templates/js-mongo/src/db/db.js

A simple CLI to scaffold Express.js starter projects.

import mongoose from 'mongoose';

import { env } from '../config/env.js';

let hasConnectionListeners = false;

/**
 * Attaches mongoose connection listeners once per process.
 *
 * Usage: call before the first `mongoose.connect` attempt.
 * Expects module-level listener state to prevent duplicate subscriptions and
 * returns `void` after wiring connected/disconnected/error observers.
 */
const attachConnectionListeners = () => {
  if (hasConnectionListeners) {
    return;
  }

  mongoose.connection.on('connected', () =>
    console.log(`Connection with "${mongoose.connection.name}" DB established 🤖.`),
  );
  mongoose.connection.on('disconnected', () =>
    console.log(`Disconnected from "${mongoose.connection.name}" DB 🔌.`),
  );
  mongoose.connection.on('error', (error) =>
    console.log(`🚨 "${mongoose.connection.name}" DB Error:`, error),
  );

  hasConnectionListeners = true;
};

/**
 * Mongo lifecycle API used by startup, readiness checks, and shutdown hooks.
 *
 * Usage: import this module in app bootstrap and signal handlers.
 * Expects validated Mongo configuration and returns async helpers for connect,
 * ping, and close operations.
 */
export default {
  connect: async () => {
    if (mongoose.connection.readyState === 1) {
      return;
    }

    attachConnectionListeners();
    await mongoose.connect(env.MONGO_DB_URI);
  },
  close: async () => {
    if (mongoose.connection.readyState === 0) {
      return;
    }

    await mongoose.disconnect();
  },
  ping: async () => {
    if (mongoose.connection.readyState !== 1 || !mongoose.connection.db) {
      throw new Error('MongoDB is not connected');
    }

    await mongoose.connection.db.admin().ping();
  },
};