$ toLong（总计）

db.orders.insert( [
   { _id: 1, item: "apple", qty: NumberInt(5) },
   { _id: 2, item: "pie", qty: "100" },
   { _id: 3, item: "ice cream", qty: NumberLong(500) },
   { _id: 4, item: "almonds", qty: "50" },
] )

// Define stage to add convertedQty field with converted qty value

qtyConversionStage = {
   $addFields: {
      convertedQty: { $toLong: "$qty" }
   }
};

// Define stage to sort documents by the converted qty values

sortStage = {
   $sort: { "convertedQty": -1 }
};


db.orders.aggregate( [
   qtyConversionStage,
   sortStage
])

{ "_id" : 1, "item" : "apple", "qty" : 5, "convertedQty" : NumberLong(5) }
{ "_id" : 2, "item" : "pie", "qty" : "100", "convertedQty" : NumberLong(100) }
{ "_id" : 3, "item" : "ice cream", "qty" : NumberLong(500), "convertedQty" : NumberLong(500) }
{ "_id" : 4, "item" : "almonds", "qty" : "50", "convertedQty" : NumberLong(50) }