🧾 Node.js – MongoDB Query – Powerful Data Retrieval Techniques with Node.js

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🧲 Introduction – What Are MongoDB Queries in Node.js?

In MongoDB, a query is how you retrieve data that matches certain conditions. Using Node.js, you can write powerful queries to search, filter, and project data from collections—essential for building APIs, admin panels, and intelligent search features.

🎯 In this guide, you’ll learn:

• How to use filter queries with MongoDB’s Node.js driver
• Combine logical operators like $and, $or, $not
• Use comparison operators ($gt, $lt, $in, etc.)
• Best practices for performance and readability

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⚙️ Setup – MongoDB Project and Connection

Install the official driver:

npm install mongodb

📁 db.js – Reusable connection module:

const { MongoClient } = require('mongodb');
const url = 'mongodb://127.0.0.1:27017';
const client = new MongoClient(url);
const dbName = 'appDB';

async function getDB() {
  await client.connect();
  console.log('✅ Connected to MongoDB');
  return client.db(dbName);
}

module.exports = getDB;

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🔍 Basic Query – Find Documents by Field Match

const getDB = require('./db');

async function findUsersByRole() {
  const db = await getDB();
  const users = await db.collection('users').find({ role: 'admin' }).toArray();
  console.log('👤 Admins:', users);
}

findUsersByRole();

✅ Fetches all users where the role equals 'admin'.

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🔎 Comparison Operators

const users = await db.collection('users').find({
  age: { $gte: 25, $lte: 40 }
}).toArray();

🎯 Retrieves users aged between 25 and 40 (inclusive).

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📛 Logical Operators – $and, $or, $not

$or Example:

const users = await db.collection('users').find({
  $or: [{ role: 'admin' }, { age: { $gt: 50 } }]
}).toArray();

✅ Matches users who are admins or age over 50.

$and Example:

const users = await db.collection('users').find({
  $and: [{ age: { $gt: 20 } }, { status: 'active' }]
}).toArray();

✅ Matches users who are older than 20 and active.

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📥 Use $in and $nin for Array Matching

const users = await db.collection('users').find({
  country: { $in: ['India', 'USA'] }
}).toArray();

✅ Matches users from either India or USA.

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🧾 Regex Queries – Pattern Matching

const users = await db.collection('users').find({
  name: { $regex: '^A', $options: 'i' }
}).toArray();

✅ Matches names that start with “A”, case-insensitive.

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📑 Project Fields Using projection

const users = await db.collection('users').find(
  { status: 'active' },
  { projection: { name: 1, email: 1, _id: 0 } }
).toArray();

✅ Returns only name and email fields.

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🧱 Best Practices for MongoDB Query in Node.js

✅ Practice	💡 Why It Matters
Use indexes on frequently queried fields	Boosts query performance
Use projections	Reduces bandwidth and improves performance
Combine filters carefully	Prevents overly broad queries
Validate user inputs	Avoids injection and malformed queries
Use cursors for large datasets	Efficient memory usage with large queries

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📌 Summary – Recap & Next Steps

MongoDB queries in Node.js are flexible and expressive. With operators like $and, $or, $in, and regex, you can filter nearly any data shape to build precise results for your apps.

🔍 Key Takeaways:

• Use find() with filters and projections for full control
• Combine operators for advanced conditions
• Use regex for flexible string matching
• Project only needed fields using { projection: { field: 1 } }

⚙️ Real-world relevance:
Used in product filters, search boxes, admin dashboards, analytics, and permission checks.

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❓FAQs – MongoDB Query in Node.js

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❓ What’s the difference between find() and findOne()?
✅ findOne() returns the first match, find() returns a cursor to all matches.

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❓ How can I use dynamic filters in Node.js?
✅ Build your query object in JavaScript before passing to find():

const filter = { age: { $gte: minAge } };

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❓ Can I query nested fields?
✅ Yes, using dot notation:

{ "address.city": "Delhi" }

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❓ How do I limit or skip documents in a query?
✅ Use .limit() and .skip():

find().skip(10).limit(5)

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❓ Is it safe to use user-provided filters?
✅ Yes, but always sanitize inputs and avoid directly inserting untrusted values.

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