db={/** Collection*/"students":[{"_id":"0","firstname":"Bert","lastname":"Holden"},{"_id":"1","firstname":"Sam","lastname":"Olsen"},{"_id":"2","firstname":"James","lastname":"Swan"}],/** Collection*/"courses":[{"_id":"10","coursename":"Databases","grades":[{student_id:"0",grade:83.442},{student_id:"1",grade:45.325},{student_id:"2",grade:87.435}]}],}

db.students.aggregate([{$match:{_id:"0"}},{$lookup:{from:"courses",pipeline:[{$unwind:"$grades"},{$match:{"grades.student_id":"0"}},{$group:{"_id":"$_id","coursename":{$first:"$coursename"},"grade":{$first:"$grades.grade"},"student_id":{$first:"$grades.student_id"}}}],as:"student_course"}}])