Performs a left outer join to an unsharded collection in the same database to filter in documents from the “joined” collection for processing. The $lookup stage does an equality match between a field from the input documents with a field from the documents of the “joined” collection.
To each input document, the $lookup stage adds a new array field whose elements are the matching documents from the “joined” collection. The $lookup stage passes these reshaped documents to the next stage.
MongoDB Documentation: https://docs.mongodb.com/manual/reference/operator/aggregation/lookup/#pipe._S_lookup
Performs a left outer join to an unsharded collection in the same database to filter in documents from the “joined” collection for processing. The $lookup stage does an equality match between a field from the input documents with a field from the documents of the “joined” collection. To each input document, the $lookup stage adds a new array field whose elements are the matching documents from the “joined” collection. The $lookup stage passes these reshaped documents to the next stage. MongoDB Documentation: https://docs.mongodb.com/manual/reference/operator/aggregation/lookup/#pipe._S_lookup