db={"job":[{"_id":ObjectId("5b0d2b2c7ac4792df69a9942"),"title":"software engineer","categories":[ObjectId("5b0d16ee7ac4792df69a9924"),ObjectId("5b0d47667ac4792df69a9994")],"deadline":ISODate("2021-05-03T06:29:54.634+00:00")}],"job_categories":[{"_id":ObjectId("5b0d16ee7ac4792df69a9924"),"name":"front-end"},{"_id":ObjectId("5b0d47667ac4792df69a9994"),"name":"full-stack"}]}

db.job.aggregate([{"$lookup":{"from":"job_categories","localField":"categories","foreignField":"_id","as":"categories_list"}},{"$project":{"title":1,"categories":1,"deadline":1,"categories_list":"$categories_list.name"}}])