Question

下面是我的示例文档：我想使用聚合查询获取最大版本的错误。

{
    "_id": {
      "objectIdentifier": {
        "identifier": {
          "Empid": "715e66c7-92ff-4619-9324-2c708489fe27"
        },
        "objectName": "EmployeeInfoValidationValue"
      },
      "Empid": "715e66c7-92ff-4619-9324-2c708489fe27"
    },
    "Versions": [
      {
        "errors": [
          {
            "level": "ERROR",
            "message": "Employee Name missing",
            "timestamp": NumberLong(1531509214154)
          }
        ],
        "resultSetId": "6314a9b1-1bb0-4ba7-8128-9db39085339c",
        "scope": "INPUT_QUALITY",
        "validationLevelSeverity": "ERROR",
        "validationResultsIdentifier": {
          "identifier": {
            "objectIdentifier": {
              "identifier": {
                "Empid": "715e66c7-92ff-4619-9324-2c708489fe27"
              },
              "objectName": "EmployeeInfoValidationValue"
            },
            "Empid": "715e66c7-92ff-4619-9324-2c708489fe27"
          },
          "objectName": "ValidationResult"
        },
        "version": NumberLong(10039)
      },
      {
        "errors": [
          {
            "level": "ERROR",
            "message": "Employee Name length is not within specified range",
            "timestamp": NumberLong(1531123789457)
          }
        ],
        "resultSetId": "8743100a-1464-46af-b4d6-6636c47c8f36",
        "scope": "INPUT_QUALITY",
        "validationLevelSeverity": null,
        "validationResultsIdentifier": {
          "identifier": {
            "objectIdentifier": {
              "identifier": {
                "Empid": "715e66c7-92ff-4619-9324-2c708489fe27"
              },
              "objectName": "EmployeeInfoValidationValue"
            },
            "Empid": "715e66c7-92ff-4619-9324-2c708489fe27"
          },
          "objectName": "ValidationResult"
        },
        "version": NumberLong(10097)
      }
    ]
  }

我编写了聚合查询，它显示了具有最高版本的所有记录-例如，显示最高版本：NumberLong(10097)。在这种情况下，我不确定如何将Versions.errors显示为“雇员姓名长度不在指定范围内”。这是我写的查询：

db.ValidationResults.aggregate(
    [
            {
            $match: { 
                "_id.Empid" : "715e66c7-92ff-4619-9324-2c708489fe27",
                "Versions.scope" : "INPUT_QUALITY"
            }
        },

        {
          $project:
            {
                versionMax: {$max: "$Versions.version"}
     }
 }
 ]
     )

我尝试$addFields来显示错误，但是它只返回null（不起作用）。 TIA

Answer 1

您可以在下一个流水线阶段将versionMax与$filter一起使用，以获取version等于$max值的单项数组。然后，您可以使用$unwind将单元素数组转换为对象：

db.ValidationResults.aggregate([
    {
        $project: {
            Versions: 1,
            MaxVersion: { $max: "$Versions.version" }
        }
    },
    {
        $project: {
            Versions: {
                $filter: {
                    input: "$Versions",
                    as: "x",
                    cond: { $eq: [ "$$x.version", "$MaxVersion" ] }
                }
            }
        }
    },
    {
        $unwind: "$Versions"
    }
])

具有$ project和$ max的Mongo Db聚合

1 个答案: