Mongodb 按动态字段对mongo集合排序

这是我的收藏：

[{"currency": "USD", "amount": 1}, 
{"currency": "EUR", "amount": 1}]

[{"currency": "USD", "amount": 1, "amount_in_USD": 1}, 
{"currency": "EUR", "amount": 1, "amount_in_USD": 1.2}]

我想创建一个新字段，并使用转换率动态排序我的集合

例如：1欧元=1.2美元。这将作为已排序（升序）集合返回：

[{"currency": "USD", "amount": 1}, 
{"currency": "EUR", "amount": 1}]

[{"currency": "USD", "amount": 1, "amount_in_USD": 1}, 
{"currency": "EUR", "amount": 1, "amount_in_USD": 1.2}]

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我认为

$average\u sales

应该更改为

$amount

我认为

$average\u sales

应该更改为

$amount