Question

我正在努力让mongodb查询正常工作。下面是我的示例集合。如您所见，图片List是一个可选的嵌套数组。

{
  "firstName" : "Mark",
  "gender" : "M",
  "PictureList":[]
},
{
  "firstName" : "Jane",
  "gender" : "F",
  "PictureList":[]
},
{
  "firstName" : "Mary",
  "gender" : "F",
  "PictureList" : [{"name" : "20151128_233939.jpg","dpInd" : "N"}, 
                   {"name" : "20150712_231715.jpg","dpInd" : "Y"}
                  ]
}

我的问题是？我需要

选择性别=＆＃34; F＆＃34;

在级别2应用另一个过滤器，仅从dpInd =＆＃34; Y＆＃34;的嵌套数组中提取记录。如果不满足此条件，则仅针对嵌套数组显示空结果。我的预期结果是

   {
      "firstName" : "Jane",
      "gender" : "F",
      "PictureList":[]
   }
   {
      "firstName" : "Mary",
      "gender" : "F",
      "PictureList" : [{"name" : "20150712_231715.jpg","dpInd" : "Y"}]
   }

Answer 1

您需要$project您的文档并使用$map运算符返回一系列与您的critera匹配的子文档，并使用$cond运算符返回false。您可以使用$setDifference运算符从数组中过滤出false。

db.people.aggregate([
    { "$match": { "gender": "F" } },
    { "$project": {
        "firstName": 1,
        "gender": 1, 
        "PictureList": {
            "$setDifference": [
                { "$map": { 
                    "input": "$PictureList", 
                    "as": "pl", 
                    "in": { 
                         "$cond": [ 
                              { "$eq": [ "$$pl.dpInd", "Y" ] }, 
                              "$$pl", 
                              false
                         ]
                    }
                }}, 
                [false]
            ]
        }
    }}
])

哪个收益率：

{
        "_id" : ObjectId("566660b147d21084f02042b3"),
        "firstName" : "Jane",
        "gender" : "F",
        "PictureList" : [ ]
}
{
        "_id" : ObjectId("566660b147d21084f02042b4"),
        "firstName" : "Mary",
        "gender" : "F",
        "PictureList" : [
                {
                        "name" : "20150712_231715.jpg",
                        "dpInd" : "Y"
                }
        ]
}

MongoDB查询：在文档中的不同级别应用条件

1 个答案: