[{user:{data:{order1:"data",order2:"data2",order3:"data3",}},},{user:{data:{order1:"data",order2:"data2",}},},{user:{data:{order1:"data",order3:"data3",}},},{user:{data:{order1:"data",order2:"data2",order3:"data3",}},},{user:{data:{order1:"data"}}}]

db.collection.aggregate([{"$match":{"$expr":{"$eq":[{"$let":{"vars":{"orderElem":{"$objectToArray":"$user.data"},},"in":"$$orderElem.k"},},["order1"],],}},}])