db={"students":[{"_id":"99881","student":{"username":"jdeterman","firstName":"Jessica","lastName":"Determan","fullName":"Jessica Determan","courseId":"MATH101","subjectId":11622,"tutorId":6744}}],"courses":[{"_id":"761","courseKeys":[{"courseId":"MATH101","name":"Basic Mathematics","subjectId":11622,"tutorId":6744,"level":1},{"courseId":"BIOSCI221","name":"Biology 2","subjectId":16643,"tutorId":6744,"level":2},{"courseId":"ALGEBRA1","name":"Algebra 1","subjectId":17733,"tutorId":2144,"level":1},{"courseId":"ALGEBRA2","name":"Algebra 2","subjectId":91100,"tutorId":3322,"level":2}]}]}

db.courses.aggregate([{$match:{_id:"761"}},{$unwind:"$courseKeys"},{$lookup:{from:"students",localField:"courseKeys.subjectId",foreignField:"student.subjectId",as:"students"}},{$unwind:"$students"},{$project:{_id:0,firstName:"$students.student.firstName",lastName:"$students.student.lastName",courseId:"$courseKeys.courseId",courseName:"$courseKeys.name",level:"$courseKeys.level"}}])