计算MongoDB中的不同值

Question

我尝试在MongoDB中计算不同的值,但我没有得到我期望的结果.

以下是数据示例:

{
        "_id" : ObjectId("55d354b0d5cec8aad571b8fe"),
        "version" : "0.4",
        "scan-time" : {
                "start" : 1439913109,
                "end" : 1439913136
        },
        "services" : [
                {
                        "service-type" : "SV1",
                        "service-version" : "V1",
                        "location" : {
                                "ipv4-address" : "192.168.1.1",
                                "protocol" : "tcp"
                        },
                        "classification-method" : "probed"
                },
                {
                        "service-type" : "SV1",
                        "service-version" : "V2",
                        "location" : {
                                "ipv4-address" : "192.168.1.2",
                                "protocol" : "tcp"
                        },
                        "classification-method" : "probed"
                },
                {
                        "location" : {
                                "ipv4-address" : "192.168.1.3",
                                "protocol" : "tcp"
                        },
                        "classification-method" : "probed",
                        "service-type" : "SV1",
                        "service-version" : "V3"
                },
                {
                        "service-type" : "SV2",
                        "service-version" : null,
                        "location" : {
                                "ipv4-address" : "192.168.1.4",
                                "protocol" : "tcp"
                        },
                        "classification-method" : "probed"
                }
        ]
}

我可以使用此查询列出所有不同的值:

db.collection.distinct("services.service-type")

但是,我还需要一个计数.我尝试过这个,但它没有给出我想要的结果:

db.collection.aggregate(
    [
       {
         $group : {
            _id : "$services.service-type",
            count: { $sum: 1 }
         }
       }
    ]
)

我需要看到这个:

SV1: 3
SV2: 1

MongoDB版本:

> db.version()
3.0.5

谢谢你的帮助!

Answer 1

要在不同的查询中使用嵌套服务数组,您需要使用$ unwind来展开$ services

以下查询将输出不同的计数:

db.collection.aggregate([     
    { $unwind: "$services" },
    {
      $group : {
         _id : { "services-service-type": "$services.service-type" },
         count: { $sum: 1 }
      }
    }
])

输出:

{
    "result" : [ 
        {
            "_id" : {
                "services-service-type" : "SV2"
            },
            "count" : 1
        }, 
        {
            "_id" : {
                "services-service-type" : "SV1"
            },
            "count" : 3
        }
    ],
    "ok" : 1
}