Node.js and MongoDB are popular technologies for creating web applications. One of the most common tasks when working with these technologies is to join data from multiple collections in MongoDB. In this tutorial, we will show you how to perform a join in Node.js using the MongoDB driver.
First, let's assume that we have two collections in MongoDB: "users" and "orders". The "users" collection contains information about users, such as their name and email, while the "orders" collection contains information about orders, such as the product name and the price.
To perform a join, we first need to connect to the MongoDB database using the MongoDB driver. Once we are connected, we can use the "aggregate" method to join the two collections. The aggregate method takes an array of pipeline stages as its first argument, and the pipeline stages define the join operation.
For example, to join the "users" and "orders" collections on the "user_id" field, we can use the following pipeline stages:
In this example, the $lookup stage joins the "users" collection with the "orders" collection on the "user_id" field. The "from" field specifies the collection to join with, the "localField" field specifies the field in the "users" collection to join on, and the "foreignField" field specifies the field in the "orders" collection to join on. The "as" field specifies the name of the new field that will be added to the "users" collection to store the joined data.
Once we have defined the pipeline stages, we can use the aggregate method to perform the join:
In this example, the aggregate method joins the "users" and "orders" collections on the "user_id" field, and the result is logged to the console.
By following these steps, you can easily join data from multiple collections in MongoDB using Node.js. This is a powerful feature that can be used to create more complex and dynamic web applications.