Database

db={"books":[{isbn:"0007",title:"Book7",pages:NumberInt("150"),price:NumberDecimal("321.2"),copies:NumberInt("3"),language:"english",author:["Author1"],category:["Space Opera"],genre:["Genre-1","Genre-2"],character:["Character-1","Character-2"]},{isbn:"0006",title:"Book6",pages:NumberInt("150"),price:NumberDecimal("321.2"),copies:NumberInt("3"),language:"english",author:["Author1"],category:["Space Opera"],genre:["Genre-1","Genre-2"],character:["Character-1","Character-2"]},{isbn:"0002",title:"Book2",pages:NumberInt("150"),price:NumberDecimal("321.2"),copies:NumberInt("3"),language:"english",author:["Author1"],category:["Space Opera"],genre:["Genre-1","Genre-2"],character:["Character-1","Character-2"]},{isbn:"0001",title:"Book1",pages:NumberInt("150"),price:NumberDecimal("321.2"),copies:NumberInt("3"),language:"english",author:["Author1"],category:["Space Opera"],genre:["Genre-1","Genre-2"],character:["Character-1","Character-2"]}],"orders":[{orderNo:"3",customerNo:"0003",date:{day:NumberInt("25"),month:NumberInt("02"),year:NumberInt("2021")},orderLine:[{isbn:"0006",price:NumberDecimal("341.0"),amount:NumberInt("2")},{isbn:"0007",price:NumberDecimal("170.5"),amount:NumberInt("1")}]},{orderNo:"4",customerNo:"0004",date:{day:NumberInt("25"),month:NumberInt("02"),year:NumberInt("2021")},orderLine:[{isbn:"0001",price:NumberDecimal("341.0"),amount:NumberInt("6")},{isbn:"0002",price:NumberDecimal("170.5"),amount:NumberInt("7")}]}]}

Query

db.books.aggregate([{$lookup:{from:"orders",let:{isbn:"$isbn"},pipeline:[{$match:{$expr:{$in:["$$isbn","$orderLine.isbn"]}}},{$project:{_id:0,amount_total:{$let:{vars:{orders:{$filter:{input:"$orderLine",cond:{$eq:["$$this.isbn","$$isbn"]}}}},in:{$sum:"$$orders.amount"}}}}}],as:"amount"}},{$project:{_id:0,isbn:1,amount_total:{$sum:"$amount.amount_total"}}}])

Result