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Node.js MongoDB Join ❮ Previous Next ❯

Join Collections

MongoDB is not a relational database, but you can perform a left outer join by using the $lookup stage.

The $lookup stage lets you specify which collection you want to join with the current collection, and which fields that should match.

Consider you have a "orders" collection and a "products" collection:

orders

[ { _id: 1, product_id: 154, status: 1 }]

products

[ { _id: 154, name: 'Chocolate Heaven' }, { _id: 155, name: 'Tasty Lemons' }, { _id: 156, name: 'Vanilla Dreams' }]

Example

Join the matching "products" document(s) to the "orders" collection:

let MongoClient = require('mongodb').MongoClient;let url = "mongodb://127.0.0.1:27017/"; MongoClient.connect(url, function(err, db) { if (err) throw err; let dbo = db.db("mydb"); dbo.collection('orders').aggregate([ { $lookup: { from: 'products', localField: 'product_id', foreignField: '_id', as: 'orderdetails' } } ]).toArray(function(err, res) { if (err) throw err; console.log(JSON.stringify(res)); db.close(); });}); Run example »

Save the code above in a file called "demo_mongodb_join.js" and run the file:

Run "demo_mongodb_join.js"

C:\Users\Your Name>node demo_mongodb_join.js

Which will give you this result:

[ { "_id": 1, "product_id": 154, "status": 1, "orderdetails": [ { "_id": 154, "name": "Chocolate Heaven" } ] }]

As you can see from the result above, the matching document from the products collection is included in the orders collection as an array.

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