mongodb Java 驱动程序 - 具有多个字段的 $group [英] mongodb Java Driver - $group with multiple fields

问题描述

我的目标是使用聚合框架创建一个管道来对我的数据进行分组，然后将此管道与 java 驱动程序一起使用.MongoDB v4.0.3

My goal is to create a pipeline using the aggregation framework to group my data and then use this pipeline with the java driver. MongoDB v4.0.3

我使用 MongoDB Compass 创建了以下管道(简化为重要部分):

I created the following pipeline using MongoDB Compass (reduced to the important part):

[{
    $group: {
        _id: {
            year: '$year',
            month: '$month',
            day: '$day',
            prodName: '$prodName',
            actionName: '$actionName'
        },
        actionCount: {
            $sum: 1
        }
    }
  }
]

这导致了以下(生成的)Java 代码:

This resulted in the following (generated) Java code:

collectionName.aggregate(
  Arrays.asList(
    group(and(eq("year", "$year"),
              eq("month", "$month"),
              eq("day", "$day"),
              eq("prodName", "$prodName"),
              eq("actionName", "$actionName")),
         sum("actionCount", 1))
);

集合中$group阶段之前的数据如下所示:

The data before the $group stage in the collection looks like this:

{
 year: 2020,
 month: 01,
 day: 01,
 prodName: "productXY",
 actionName: "actionXY"
}

$group 阶段应该返回以下数据结构:

The $group stage should return the following data structure:

{
  _id: {
    year: 2020,
    month: 01,
    day: 01,
    prodName: "productXY",
    actionName: "actionXY"
  },
  actionCount: 50
}

问题

Mongo Compass 预览阶段的结果符合预期，但是使用java驱动的阶段的结果有很大的不同.它只返回 1 个文档(而不是预期的 20 个)并且只返回字段 actionCount.

Mongo Compass previews the result of the stage as expected, but the results of the stage using the java driver are very different. It only returns 1 Document (instead of 20 expected) and only returns the field actionCount.

问题

如何更改 java 代码以创建所需的管道阶段?

How do I have to change the java code to create the desired pipeline stage?

推荐答案

我找到了解决方案.我需要将 and 运算符更改为 Projections.fields 运算符.我仍然不知道为什么.也许其他人可以详细说明这一点.

I found the solution. I needed to change the and operator to a Projections.fields operator. I still don't know why. Maybe someon else can elaborate about that.

所以工作查询看起来像这样:

So the working query looks like this:

collectionName.aggregate(
  Arrays.asList(
    group(fields(eq("year", "$year"),
                 eq("month", "$month"),
                 eq("day", "$day"),
                 eq("prodName", "$prodName"),
                 eq("actionName", "$actionName")),
         sum("actionCount", 1))
);

这篇关于mongodb Java 驱动程序 - 具有多个字段的 $group的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！