Java MongoDB聚合 - 多个字段的总和

Question

我正在尝试使用 Java 执行 mongodb 聚合，但无法弄清楚如何分别对 2 个字段求和。以下是我的文档结构：

{
    "_id" : ObjectId("59b6b96423b65d0a04de128d"),
    "itemCount": 25,
    "defectiveItemCount": 5,
    "time": ISODate("x")
},
{
    "_id" : ObjectId("59b6b96423b65d0a04de128d"),
    "itemCount": 20,
    "defectiveItemCount": 7,
    "time": ISODate("x")
}

我正在尝试使用：

Aggregation pipeline = newAggregation(
        match(Criteria.where("time").gt(time)),
        group().sum("itemCount").as("total"),
        group().sum("defectiveItemCount").as("defective"),
        project("total").and("defective").previousOperation()
);

我也试过了：

Aggregation pipeline = newAggregation(
        match(Criteria.where("time").gt(time)),
        group().sum("itemCount").as("total").sum("defectiveItemCount").as("defective"),
        project("total").and("defective").previousOperation()
);

当我运行此聚合时，缺陷的结果始终为 NULL。

我想要的结果是：

{
    "itemCount": 45,
    "defectiveItemCount": 12
}

以上是否可行或者我应该执行 2 个单独的聚合？

Answer 1

您必须在组中附加累加器。

类似

Aggregation pipeline = newAggregation(
     match(Criteria.where("time").gt(time)),
     group().sum("itemCount").as("total").sum("defectiveItemCount").as("defective"),
     project("total","defective")
 );