the name of the new array field to add to the input documents
the field from the documents in the from collection
the collection to perform the join with
the field from the documents input
_Since MongoDB 3.2:_ Performs a left outer join to an unsharded collection in the same database to filter in documents from the "joined" collection for processing. https://docs.mongodb.com/v3.2/reference/operator/aggregation/lookup/#pipe._S_lookup
the collection to perform the join with
the field from the documents input
the field from the documents in the
fromcollectionthe name of the new array field to add to the input documents