Connect MongoDB & PostgreSQL in Node.js

Connecting your database might sound simple, “paste the URI and go,” right?
However, as your app grows, a sloppy connection setup can lead to timeouts, hanging requests, or silent disconnections.
Let’s fix that from the start.

What You’ll Learn

• How to connect Node.js with MongoDB (via Mongoose)

• How to connect Node.js with PostgreSQL (via pg)

• Proper async setup

• Handle errors, timeouts, and disconnects

• Write connection code you can actually reuse in production

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MongoDB Connection (with Mongoose)

Mongoose is the go-to library for Node.js + MongoDB. It simplifies schema management and handles async connections.

1 Install dependencies

npm install mongoose

2 Create a connection file

Let’s call it db/mongo.js

import mongoose from "mongoose";

const MONGO_URI = process.env.MONGO_URI || "mongodb://localhost:27017/myapp";

export async function connectMongo() {
  try {
    // Set connection options
    const options = {
      useNewUrlParser: true,
      useUnifiedTopology: true,
      serverSelectionTimeoutMS: 5000, // Timeout after 5s
    };

    await mongoose.connect(MONGO_URI, options);
    console.log("✅ MongoDB connected successfully");
  } catch (err) {
    console.error("❌ MongoDB connection error:", err.message);
    process.exit(1);
  }

  // Handle runtime errors
  mongoose.connection.on("error", (err) => {
    console.error("⚠️ MongoDB connection error:", err);
  });

  mongoose.connection.on("disconnected", () => {
    console.warn("🔌 MongoDB disconnected");
  });
}

3 Use it in your app

import express from "express";
import { connectMongo } from "./db/mongo.js";

const app = express();

await connectMongo();

app.listen(3000, () => console.log("🚀 Server running on port 3000"));

---

PostgreSQL Connection (with pg)

PostgreSQL uses the official pg package. Simple and solid.

1 Install dependencies

npm install pg

2 Create a connection file

db/postgres.js

import pkg from "pg";
const { Pool } = pkg;

const POSTGRES_URI = process.env.POSTGRES_URI || "postgresql://user:password@localhost:5432/myapp";

const pool = new Pool({
  connectionString: POSTGRES_URI,
  idleTimeoutMillis: 5000, // Close idle clients after 5s
  connectionTimeoutMillis: 5000, // Timeout after 5s if cannot connect
});

pool.on("connect", () => console.log("✅ PostgreSQL connected successfully"));

pool.on("error", (err) => {
  console.error("❌ Unexpected PostgreSQL error:", err);
  process.exit(-1);
});

export async function query(text, params) {
  const client = await pool.connect();
  try {
    const res = await client.query(text, params);
    return res;
  } catch (err) {
    console.error("⚠️ Query error:", err.message);
    throw err;
  } finally {
    client.release();
  }
}

3 Use it in your app

import express from "express";
import { query } from "./db/postgres.js";

const app = express();

app.get("/", async (req, res) => {
  const result = await query("SELECT NOW()");
  res.send(result.rows);
});

app.listen(3000, () => console.log("🚀 Server running on port 3000"));

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Quick Tips

• Always wrap connections in async functions

• Use env variables for credentials never hardcode them

• Add timeouts so your app doesn’t hang forever

• Use event listeners (on('error'), on('disconnected')) to handle runtime issues

• For real projects, add a reconnection logic if needed

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Example .env file

MONGO_URI=mongodb://localhost:27017/myapp
POSTGRES_URI=postgresql://user:password@localhost:5432/myapp

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Wrap-Up

Connecting to a database isn’t just about making it work. It’s about ensuring stability, so your app remains operational even when the database restarts or the network experiences hiccups.