db={"tasks_list":[{"_id":ObjectId("61c03dfb47370c024193afde"),"name":"complete unit 2","createBy":ObjectId("61c03f6b47370c024193afe0")}],"users":[{"_id":ObjectId("61c03f6b47370c024193afe0"),"name":"admin","image":"img_default.jpg"}]}

db.tasks_list.aggregate([{"$lookup":{"from":"users","localField":"createBy","foreignField":"_id","as":"createBy"}},{"$set":{"createBy":{"$first":"$createBy"}}}])