db={"persons":[{"person_id":1,"person_name":"John"}],"jobs":[{"job_id":21,"person_id":1,"job":"Teacher"}]}

db.persons.aggregate([{"$lookup":{"from":"jobs","localField":"person_id","foreignField":"person_id","as":"job_docs"}},{"$project":{"person_id":1,"person_name":1,"job":{"$first":"$job_docs.job"}}}])