db={"Audios":[{"_id":"5f6b1a2e69eef14818ca03a7","audioURL":"https://boyd.org","state":"draft",},{"_id":"5f6b1e1c6297f34bc6f1fee3","name":"navigate","audioURL":"http://mariane.org","state":"draft",},{"_id":"5f5b5423ba39f738d593b504","audioURL":"https://storage/test123mp31599820832928.mp3","state":"draft",}],"Lessons":[{"_id":"5f770e275cef7a611f3cf931","minigameDescriptions":[{"assessmentSections":[{"mark":"step_1","start":1,"end":2,"stepAudio":{"backingTrackAudioId":"5f6b1a2e69eef14818ca03a7","previewTrackAudioId":"5f6b1a2e69eef14818ca03a7"}},{"mark":"step_2","start":3,"end":6,"stepAudio":{"backingTrackAudioId":"5f6b1e1c6297f34bc6f1fee3","previewTrackAudioId":"5f6b1e1c6297f34bc6f1fee3"}},{"mark":"step_3","start":7,"end":10,"stepAudio":{"backingTrackAudioId":"5f6b1a2e69eef14818ca03a7","previewTrackAudioId":"5f5b5423ba39f738d593b504"}}],"drumStyleName":"DrumStyleHalftimeShuffle","onboarding":false,"showHints":false,"minigameType":"StrummingTrainer",}],"_updated_at":"2020-10-02T12:00:23.848Z",}]}

db.Lessons.aggregate([{$unwind:"$minigameDescriptions"},{$unwind:"$minigameDescriptions.assessmentSections"},{$lookup:{from:"Audios",let:{audioId:"$minigameDescriptions.assessmentSections.stepAudio.previewTrackAudioId"},pipeline:[{$match:{$expr:{$eq:["$_id","$$audioId"]}}}],as:"minigameDescriptions.assessmentSections.stepAudio.previewTrackAudio"}},{$group:{_id:{_id:"$_id",/** assId: "$minigameDescriptions.assessmentSections.mark"*/},assessmentSections:{$addToSet:"$minigameDescriptions.assessmentSections"},drumStyleName:{$first:"$minigameDescriptions.drumStyleName"},minigameType:{$first:"$minigameDescriptions.minigameType"}}},{$group:{_id:"$_id",minigameDescriptions:{$addToSet:{assessmentSections:"$assessmentSections",drumStyleName:"$drumStyleName",minigameType:"$minigameType"}}}}])