db={"venue":[{"_id":"2","name":"name2"},{"_id":"3","name":"name3"},{"_id":"4","name":"name4"},{"_id":"5","name":"name5"}],"user":[{"_id":"u2","name":"u2",venue_id:"2"},{"_id":"u3","name":"u3",venue_id:"2"},{"_id":"u4","name":"u4",venue_id:"3"},{"_id":"u5","name":"u5",venue_id:"4"}],"show":[{"_id":"s2","name":"s2",host_id:"u2","duration":20},{"_id":"s3","name":"s3",host_id:"u2","duration":50},{"_id":"s4","name":"s4",host_id:"u2","duration":60},{"_id":"s5","name":"s5",host_id:"u4","duration":30}]}

db.venue.aggregate([{"$lookup":{"from":"user","localField":"_id","foreignField":"venue_id","as":"userLookup"}},{"$unwind":{path:"$userLookup",preserveNullAndEmptyArrays:true}},{"$lookup":{"from":"show","localField":"userLookup._id","foreignField":"host_id","as":"showLookup"}},{"$unwind":{path:"$showLookup",preserveNullAndEmptyArrays:true}},{$group:{_id:"$_id",name:{$first:"$name"},duration:{$sum:"$showLookup.duration"}}}])