NodeJs MongoDB Query

Last modified on: October 19, 2024

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<h3>Querying Documents in MongoDB with Node.js</h3>
<p>Querying documents in MongoDB is essential for retrieving data based on specific criteria. This guide will demonstrate how to perform various types of queries using Node.js, focusing on finding documents in a MongoDB collection.</p>
<hr />
<h3>Prerequisites</h3>
<ul>
<li>Ensure you have Node.js installed on your machine.</li>
<li>Have MongoDB installed and running, or use a cloud MongoDB service like MongoDB Atlas.</li>
<li>Create a new Node.js project or use an existing one.</li>
</ul>
<h3>1. Set Up Your Node.js Project</h3>
<p>If you haven't already, create a new Node.js project and install the MongoDB driver:</p>
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<pre class="language-javascript"><code>mkdir my-node-mongodb-app
cd my-node-mongodb-app
npm init -y
npm install mongodb
</code></pre>
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<h3>2. Create <code>app.js</code></h3>
<p>Create a file named <code>app.js</code>:</p>
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<pre class="language-javascript"><code>touch app.js
</code></pre>
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<h3>3. Basic Structure of <code>app.js</code></h3>
<p>Open <code>app.js</code> and set up the basic structure to connect to MongoDB:</p>
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<pre class="language-javascript"><code>const { MongoClient } = require('mongodb');

const uri = 'mongodb://localhost:27017'; // Replace with your MongoDB connection string
const client = new MongoClient(uri);

async function run() {
    try {
        // Connect to the MongoDB cluster
        await client.connect();
        console.log('Connected to MongoDB');

// Create or switch to the database and collection
        const database = client.db('mydatabase');
        const collection = database.collection('users');

// Add your query logic here

} catch (error) {
        console.error('Error connecting to MongoDB:', error);
    } finally {
        await client.close();
    }
}

run().catch(console.error);
</code></pre>
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<h3>4. Querying Documents</h3>
<h4>Step 1: Find All Documents</h4>
<p>To retrieve all documents from the collection:</p>
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<pre class="language-javascript"><code>const allUsers = await collection.find().toArray();
console.log('All Users:', allUsers);
</code></pre>
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<h4>Step 2: Find a Single Document</h4>
<p>To find a single document based on a specific condition:</p>
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<pre class="language-javascript"><code>const specificUser = await collection.findOne({ name: 'Alice' });
console.log('Specific User:', specificUser);
</code></pre>
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<h4>Step 3: Find Documents with Conditions</h4>
<p>You can use various operators to filter results. For example, to find users with a specific email domain:</p>
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<pre class="language-javascript"><code>const usersWithDomain = await collection.find({ email: { $regex: /example\.com$/ } }).toArray();
console.log('Users with example.com email:', usersWithDomain);
</code></pre>
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<h4>Step 4: Combine Conditions</h4>
<p>You can combine multiple conditions using logical operators. For example, to find users named "Alice" or with an age greater than 25:</p>
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<pre class="language-javascript"><code>const combinedQuery = await collection.find({
    $or: [{ name: 'Alice' }, { age: { $gt: 25 } }]
}).toArray();
console.log('Users named Alice or older than 25:', combinedQuery);
</code></pre>
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<h4>Step 5: Projecting Specific Fields</h4>
<p>To limit the fields returned, use the <code>projection</code> option:</p>
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<pre class="language-javascript"><code>const limitedFields = await collection.find({}, { projection: { name: 1, email: 1 } }).toArray();
console.log('Limited Fields:', limitedFields);
</code></pre>
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<h4>Step 6: Pagination</h4>
<p>To implement pagination, use the <code>skip</code> and <code>limit</code> methods:</p>
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<pre class="language-javascript"><code>const paginatedUsers = await collection.find().skip(5).limit(5).toArray();
console.log('Paginated Users:', paginatedUsers);
</code></pre>
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<h3>5. Complete Example of <code>app.js</code></h3>
<p>Here&rsquo;s how your <code>app.js</code> might look after adding the querying logic:</p>
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<pre class="language-javascript"><code>const { MongoClient } = require('mongodb');

const uri = 'mongodb://localhost:27017'; // Replace with your MongoDB connection string
const client = new MongoClient(uri);

async function run() {
    try {
        await client.connect();
        console.log('Connected to MongoDB');

const database = client.db('mydatabase');
        const collection = database.collection('users');

// Find all documents
        const allUsers = await collection.find().toArray();
        console.log('All Users:', allUsers);

// Find a specific document
        const specificUser = await collection.findOne({ name: 'Alice' });
        console.log('Specific User:', specificUser);

// Find documents with conditions
        const usersWithDomain = await collection.find({ email: { $regex: /example\.com$/ } }).toArray();
        console.log('Users with example.com email:', usersWithDomain);

// Combine conditions
        const combinedQuery = await collection.find({
            $or: [{ name: 'Alice' }, { age: { $gt: 25 } }]
        }).toArray();
        console.log('Users named Alice or older than 25:', combinedQuery);

// Projecting specific fields
        const limitedFields = await collection.find({}, { projection: { name: 1, email: 1 } }).toArray();
        console.log('Limited Fields:', limitedFields);

// Pagination
        const paginatedUsers = await collection.find().skip(5).limit(5).toArray();
        console.log('Paginated Users:', paginatedUsers);

} catch (error) {
        console.error('Error connecting to MongoDB:', error);
    } finally {
        await client.close();
    }
}

run().catch(console.error);
</code></pre>
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<h3>6. Run the Application</h3>
<p>Execute the following command in your terminal:</p>
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<pre class="language-javascript"><code>node app.js
</code></pre>
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<p>You should see the results of the various queries printed to the console.</p>
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<h3>Conclusion</h3>
<p>Querying documents in MongoDB with Node.js is a powerful way to retrieve and manipulate data. This guide provides a comprehensive overview of various query methods, allowing you to find documents based on specific conditions, project fields, and paginate results.</p>
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