Question

json下面代表我的集合的文档结构。

{
    "_id" : ObjectId("591a653c366df19100ed0fbc"),
    "sno" : 1,
    "chapterName" : "chapter 1: Express JS",
    "overView" : "Overview of Express JS",
    "sections" : [
            {
                    "title" : "The Node.js philosophy",
                    "subSections" : [
                            {
                                    "sno" : 1,
                                    "title" : "Small core 1",
                                    "content" : "The Node.js core itself has its foundations 1"
                            },
                            {
                                    "sno" : 2,
                                    "title" : "Small core 2",
                                    "content" : "The Node.js core itself has its foundations 2"
                            }
                    ]
            },
            {
                    "title" : "The Node.js philosophy 2",
                    "subSections" : [
                            {
                                    "sno" : 1,
                                    "title" : "Small core 1",
                                    "content" : "The Node.js core itself has its foundations 1"
                            },
                            {
                                    "sno" : 2,
                                    "title" : "Small core 2",
                                    "content" : "The Node.js core itself has its foundations 2"
                            }
                    ]
            }
    ]
}

我想写一个查询，它将以下面提到的方式返回所有记录的数据（不包括＆＃34;内容＆＃34;）

{
    "_id" : ObjectId("591a653c366df19100ed0fbc"),
    "sno" : 1,
    "chapterName" : "chapter 1: Express JS",
    "overView" : "Overview of Express JS",
    "sections" : [
            {
                    "title" : "The Node.js philosophy",
                    "subSections" : [
                            {
                                    "sno" : 1,
                                    "title" : "Small core 1"

                            },
                            {
                                    "sno" : 2,
                                    "title" : "Small core 2"

                            }
                    ]
            },
            {
                    "title" : "The Node.js philosophy 2",
                    "subSections" : [
                            {
                                    "sno" : 1,
                                    "title" : "Small core 1"

                            },
                            {
                                    "sno" : 2,
                                    "title" : "Small core 2"

                            }
                    ]
            }
    ]
}

知道如何实现这个目标吗？

Answer 1

可行，但“不是微不足道的”。这需要大量使用$map和.aggregate()

db.collection.aggregate([
    { "$project": {
      "sno": 1,
      "chapterName": 1,
      "overView": 1,
      "sections": {
        "$map": {
          "input": "$sections",
          "as": "section",
          "in": {
            "title": "$$section.title",
            "subSections": {
              "$map": {
                "input": "$$section.subSections",
                "as": "subSection",
                "in": {
                  "sno": "$$subSection.sno",
                  "title": "$$subSection.title"
                }
              }
            }
          }
        }
      }
    }}
])

我只是想提一下“扁平化”，除了考虑为什么不使用嵌套数组的所有其他考虑之外，只需考虑这些数据：

{ 
  "_id" : ObjectId("5921745d13fbc408ee20a60a"),
  "a" : 1, 
  "b" : [
    { "a" : 1, "b" : 2, "c" : 3 }, 
    { "a" : 4, "b" : 5, "c" : 6 }
  ]
}

由于这只是一个深度的数组级别，如果我想要排除"c"属性，那么我需要做的就是：

db.collection.find({},{ "b.c": 0 })

我当然得到了：

{ 
  "_id" : ObjectId("5921745d13fbc408ee20a60a"),
  "a" : 1, 
  "b" : [
    { "a" : 1, "b" : 2 }, 
    { "a" : 4, "b" : 5 }
  ]
}

这显然比在聚合投影中嵌套$map语句简单得多。

深思熟虑。

查询以排除MongoDB中的数组列

1 个答案: