MongoDB $lookup example | join multiple collection using MongoDB | sub query to join collection.

Performs a left outer join to a collection in the same database to filter in documents from the "joined" collection for processing. The $lookup stage adds a new array field to each input document. The new array field contains the matching documents from the "joined" collection. The $lookup stage passes these reshaped documents to the next stage. The aggregation pipeline stage $lookup makes it possible to join data from an input collection (the collection you’re running the query on) and a lookup collection (the collection you want data from), as long as both collections are on the same database. https://www.mongodb.com/docs/manual/reference/operator/aggregation/lookup/ #monngodb, #lookup , #joincollection