Node.js MongoDB Query

Querying is a key operation in MongoDB to retrieve documents based on specific conditions. Using Node.js and the mongodb driver, you can perform complex and efficient queries to interact with your database.

 

Key Features of MongoDB Query

1. Flexible Filters: Query documents using operators like $eq, $gt, $regex, and more.
2. Projection: Retrieve only the fields you need to optimize performance.
3. Sorting and Pagination: Control the order and quantity of results returned.

 

Step 1 Prerequisites

Ensure MongoDB is installed and running, and the mongodb package is installed in your project.

npm install mongodb

Step 2 Query with Simple Filters

Retrieve documents that match basic conditions using key-value pairs.

Example Code

const { MongoClient } = require('mongodb');

// Connection URL and Database Name
const url = 'mongodb://127.0.0.1:27017';
const dbName = 'mydatabase';

async function simpleQuery() {
  const client = new MongoClient(url);

  try {
    await client.connect();
    const db = client.db(dbName);
    const collection = db.collection('users');

    // Find documents where name is 'Alice'
    const result = await collection.find({ name: 'Alice' }).toArray();
    console.log('Query Result:', result);
  } finally {
    await client.close();
  }
}

simpleQuery().catch(console.error);

Output:

[
  { "_id": 1, "name": "Alice", "age": 28 }
]

Step 3 Query with Comparison Operators

Use comparison operators to match ranges or patterns.

Example Code

async function queryWithOperators() {
  const client = new MongoClient(url);

  try {
    await client.connect();
    const db = client.db(dbName);
    const collection = db.collection('users');

    // Find users older than 30
    const result = await collection.find({ age: { $gt: 30 } }).toArray();
    console.log('Users older than 30:', result);
  } finally {
    await client.close();
  }
}

queryWithOperators().catch(console.error);

Output:

[
  { "_id": 2, "name": "Bob", "age": 35 }
]

Step 4 Query with Logical Operators

Combine multiple conditions using logical operators like $and and $or.

Example Code

async function queryWithLogicalOperators() {
  const client = new MongoClient(url);

  try {
    await client.connect();
    const db = client.db(dbName);
    const collection = db.collection('users');

    // Find users who are either older than 30 or named 'Alice'
    const result = await collection.find({
      $or: [{ age: { $gt: 30 } }, { name: 'Alice' }]
    }).toArray();
    console.log('Logical Query Result:', result);
  } finally {
    await client.close();
  }
}

queryWithLogicalOperators().catch(console.error);

Output:

[
  { "_id": 1, "name": "Alice", "age": 28 },
  { "_id": 2, "name": "Bob", "age": 35 }
]

Step 5 Query with Regex

Use the $regex operator to perform pattern matching.

Example Code

async function queryWithRegex() {
  const client = new MongoClient(url);

  try {
    await client.connect();
    const db = client.db(dbName);
    const collection = db.collection('users');

    // Find users whose name starts with 'A'
    const result = await collection.find({ name: { $regex: '^A' } }).toArray();
    console.log('Regex Query Result:', result);
  } finally {
    await client.close();
  }
}

queryWithRegex().catch(console.error);

Output:

[
  { "_id": 1, "name": "Alice", "age": 28 }
]

Step 6 Query with Projection

Specify which fields to include or exclude in the result using projection.

Example Code

async function queryWithProjection() {
  const client = new MongoClient(url);

  try {
    await client.connect();
    const db = client.db(dbName);
    const collection = db.collection('users');

    // Retrieve only the name field
    const result = await collection.find({}, { projection: { name: 1, _id: 0 } }).toArray();
    console.log('Projection Query Result:', result);
  } finally {
    await client.close();
  }
}

queryWithProjection().catch(console.error);

Output:

[
  { "name": "Alice" },
  { "name": "Bob" }
]

Step 7 Sort and Limit Results

Control the number of results and their order using sort and limit.

Example Code

async function queryWithSortAndLimit() {
  const client = new MongoClient(url);

  try {
    await client.connect();
    const db = client.db(dbName);
    const collection = db.collection('users');

    // Retrieve 1 user sorted by age descending
    const result = await collection.find({})
      .sort({ age: -1 })
      .limit(1)
      .toArray();
    console.log('Sorted and Limited Query Result:', result);
  } finally {
    await client.close();
  }
}

queryWithSortAndLimit().catch(console.error);

Output:

[
  { "_id": 2, "name": "Bob", "age": 35 }
]

 

Summary

MongoDB provides powerful query capabilities through Node.js, enabling developers to fetch documents using filters, operators, and projections. Features like sorting and logical queries enhance flexibility, allowing for efficient data management in applications.