[{"Order_Info":[{"Line_Info":[{"Product_Info":{Product_Name:"a","Product_Cost":100,}},{"Product_Info":{Product_Name:"b","Product_Cost":50,}},{"Product_Info":{Product_Name:"c","Product_Cost":2,}}]},{"Line_Info":[{"Product_Info":{Product_Name:"d","Product_Cost":500,}}]}]},{"Order_Info":[{"Line_Info":[{"Product_Info":{Product_Name:"e","Product_Cost":30}}]}]}]

db.collection.aggregate([{$project:{Order_Info:{$map:{input:"$Order_Info",in:{$filter:{input:"$$this.Line_Info",cond:{$gt:["$$this.Product_Info.Product_Cost",30]}}}}}}}])