db={"customers":[{"id":100,"name":"a"},{"id":200,"name":"b"},{"id":300,"name":"c"},{"id":400,"name":"d"}],"sales":[{"sale_id":9999,"persons_related":[{"id":100},{"id":900},{"id":800}]},{"sale_id":9998,"persons_related":[{"id":500},{"id":550},{"id":560}]},]}

db.customers.aggregate([{$match:{id:100}},{$lookup:{from:"sales",localField:"id",foreignField:"persons_related.id",as:"sales"}}])