Understanding $lookup Concept

The $lookup stage in MongoDB is a versatile and effective tool suitable for various usage scenarios. For example, you can utilize it to merge a collection with a reference data collection, enriching your documents with additional information. Similarly, it empowers you to integrate data from two collections seamlessly, enabling the creation of comprehensive reports such as a customer order report.

To use the $lookup stage, you need to specify the following parameters:

• from: Denotes the name of the collection that will be merged with the existing one.
• localField: Represents the current collection’s field acting as the join key.
• foreignField: Specifies the field from the “from” collection serving as the join key.
• as: Refers to the name of the new array field in the resulting document, containing the outcomes of the join operation.

One of the essential stages of the Aggregation Pipeline is the $lookup. It enables us to accomplish a left outer join between two collections. This step is quite beneficial when we have to compose data from different collections into a single document. The Aggregation Pipeline in MongoDB is a robust tool that allows us to manipulate and analyze data stored in a MongoDB collection.

In this article, we’ll learn how to use the $lookup operator in aggregation pipelines in detail.