Step-by-Step Guide: Joining Collections with Node.js
To perform a collection join in MongoDB using Node.js, follow these steps:
Step 1: Create a NodeJS Application using the below command:
npm init - y
Step 2: Connect to MongoDB
Use the mongodb npm package to establish a connection to your MongoDB database.
Step 3: Perform the $lookup
Operation Use the aggregate method on your collection to perform the $lookup operation with the desired parameters.
Step 4: Handle the Result
Process the result of the join operation as needed within your Node.js application.
Example: Here’s an example of joining “orders” with “customers” collections using $lookup:
// performJoin.js
const { MongoClient } = require("mongodb");
// Connection URI
const uri = "mongodb://localhost:27017";
// Database Name
const dbName = "mydatabase";
async function performCollectionJoin() {
const client = new MongoClient(uri, { useUnifiedTopology: true });
try {
// Connect to MongoDB
await client.connect();
// Get reference to the database
const db = client.db(dbName);
// Perform $lookup aggregation to join orders with products
const result = await db
.collection("orders")
.aggregate([
{
$lookup: {
from: "products",
localField: "product_id",
foreignField: "_id",
as: "orderdetails",
},
},
])
.toArray();
console.log(result);
} catch (error) {
console.error("Error performing collection join:", error);
} finally {
// Close the MongoDB connection
await client.close();
}
}
// Call the function to perform collection join
performCollectionJoin();
// insertData.js
const { MongoClient } = require("mongodb");
// Connection URI
const uri = "mongodb://localhost:27017";
// Database Name
const dbName = "mydatabase";
// Sample data for orders collection
const orders = [
{ _id: 1, product_id: 101, quantity: 2 },
{ _id: 2, product_id: 102, quantity: 1 },
{ _id: 3, product_id: 103, quantity: 3 },
];
// Sample data for products collection
const products = [
{ _id: 101, name: "Product A", price: 20 },
{ _id: 102, name: "Product B", price: 30 },
{ _id: 103, name: "Product C", price: 25 },
];
async function createDatabaseAndInsertData() {
const client = new MongoClient(uri, { useUnifiedTopology: true });
try {
// Connect to MongoDB
await client.connect();
// Get reference to the database
const db = client.db(dbName);
// Create orders collection and insert sample data
const ordersCollection = db.collection("orders");
await ordersCollection.insertMany(orders);
// Create products collection and insert sample data
const productsCollection = db.collection("products");
await productsCollection.insertMany(products);
console.log("Sample data inserted successfully.");
} catch (error) {
console.error("Error inserting sample data:", error);
} finally {
// Close the MongoDB connection
await client.close();
}
}
// Call the function to create database and insert sample data
createDatabaseAndInsertData();
Output:
output
How to Join Two Collections in Mongodb using Node.js ?
Joining two collections in MongoDB using Node.js can be accomplished using the aggregation framework. The $lookup stage in the aggregation pipeline allows you to perform a left outer join to another collection in the same database.