如何在 MongoDB 中有条件地显示/隐藏字段

Posted 2023-05-08

【中文标题】如何在 MongoDB 中有条件地显示/隐藏字段

【英文标题】：How to Show/Hide Fields conditionally in MongoDB

【发布时间】：2021-08-08 06:26:50

【问题描述】：

非常感谢您的帮助，当列的值为空时，我正在尝试使用以下查询隐藏列。

错误：

未捕获的异常：错误：命令失败： “好”：0， "errmsg" : "由 :: Unrecognized expression '$OpenDate' 引起的 $project :: 无效", “代码”：168， "codeName" : "InvalidPipelineOperator"

文档：

"_id" : ObjectId("60f113b2211038b4b688c3e8"),
        "URN" : 103600,
        "LANAME" : "HTOL",
        "LA" : 311,
        "ESTAB" : 2014,
        "LAESTAB" : 3062352,
        "School_Name" : "Good Day Infant School",
        "Address" : 
                "Street" : "Lodge Road",
                "Locality" : "",
                "Address3" : "",
                "Town" : "London",
                "PostCode" : "CR9 20P"
        ,
        "Status" : "Open",
        "OpenDate" : "",
        "CloseDate" : "",
        "MINORGROUP" : "Maintained school",
        "SCHOOLTYPE" : "Community school",
        "ISPRIMARY" : 1,
        "ISSECONDARY" : 0,
        "ISPOST16" : 0,
        "AGELOW" : 3,
        "AGEHIGH" : 7,
        "GENDER" : "Mixed",
        "RELCHAR" : "Does not apply",
        "ADMPOL" : "Not applicable"

查询 1：

db.schools.aggregate(
                     [
                      $project:
                               OpenDate:$cond:if:$eq:["$OpenDate",""],then:0,else:1
                      
                    ]
                   )

查询 2：

db.schools.aggregate(
                     [
                      
                       $project:
                                
                                   OpenDate: $cond:["$OpenDate":"",0,1] 
                                     
                                
                     
                     ]
                   )

【问题讨论】：

看$cond的正确语法，你的实现无效。

看看这是否有用meta.stackexchange.com/questions/5234/…

【参考方案1】：

你可以使用$$REMOVE

db.collection.aggregate([
  
    $project: 
      OpenDate: 
        $cond: [
          
            $eq: [
              "$OpenDate",
              ""
            ]
          ,
          "$$REMOVE",
          "$OpenDate"
        ]
      
    
  
])

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