Mongo offers outer left joins through $lookup, now even with sub-queries. https://docs.mongodb.com/manual/reference/operator/aggregation/lookup/#specify-multip

Mongo offers outer left joins through $lookup, now even with sub-queries. https://docs.mongodb.com/manual/reference/operator/aggregation/lookup/#specify-multiple-join-conditions-with-lookup https://docs.mongodb.com/manual/reference/operator/aggregati... It also offers recursive left outer joins with $graphLookup.