select 计算 MongoDB 中的子查询

Question

这是我在 MongoDB 中的查询：

{ runCommand : 
    { aggregate : 'record', 
      pipeline : [ 
        {  $match : {  "_id" : {
              "$binary" : "HUjjlL5SCpVKNVnedOk+nQ==", "$type" : "3"
              }}},
        { $project : { Results : 1 }},
        { $unwind  : '$Results'}
       ],
     cursor: {}
}
}

我想向 "Result.Type" = "SpecificResult".

的 COUNT 个结果添加子查询

这是文档示例：

{
"_id": Binary("HUjjlL5SCpVKNVnedOk+nQ==", 3),
"Header": {
    "FileFormatVersion": "2.0",
    "Filename": "1231434534654",
    "ReferenceNumber": "235423645677"
},
"Results": [
    {
        "Type": "Title",
        "Seq": "1111",
        "Title": "Some Title",
        "SubTitle": "",
        "TitleLevel": "1"
    },
    {
        "Type": "Title",
        "Seq": "056330010",
        "Title": "Some Subtitle",
        "SubTitle": "",
        "TitleLevel": "2"
    },
    {
        "Type": "Result",
        "Seq": "0560002200040",
        "ResultValue": "value"
    },
     {
        "Type": "SpecificResult",
        "Seq": "0123234010",
        "Title": "",
        "Name": "Name",
        "ResultComments": "Comment1"
    },
     {
        "Type": "SpecificResult",
        "Seq": "0123234010",
        "Title": "",
        "Name": "Name222",
        "ResultComments": "Comment1"
    }
]
}

在 SQL 中看起来像：

SELECT *, (select count (*) from Results where Type = 'SpecificResult') FROM Results;

如何在 MongoDB 中执行此操作？

Answer 1

$filter 迭代 Results.Type 数组的循环，检查条件是否类型与 SpecificResult 匹配，$size 获取 $filter 返回结果的计数,

{ 
    runCommand : { 
        aggregate : 'record', 
        pipeline : [ 
            { $match : { "_id" : { "$binary" : "HUjjlL5SCpVKNVnedOk+nQ==", "$type" : "3" } } },
            { 
                $project : { 
                    Results : 1,
                    ResultCount: {
                        $size: {
                            $filter: {
                                input: "$Results.Type",
                                cond: { $eq:["$$this", "SpecificResult"] }
                            }
                        }
                    }
                }
            },
            { $unwind  : '$Results' }
        ],
        cursor: {}
    }
}

select 计算 MongoDB 中的子查询

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