我一直在尝试这些例子:https://docs.mongodb.com/manual/reference/operator/aggregation/push/和https://docs.mongodb.com/manual/reference/operator/aggregation/addToSet/示例文档:{"_id":1,"item":"abc","price":10,"quantity":2,"date":ISODate("2014-01-01T08:00:00Z")}{"_id":2,"item":"jkl","price":20,"quantity":1,"date":I