如果在 mongodb 中不匹配，如何删除空文档？答案

【问题标题】：how to remove empty document if it not matched in mongodb?如果在 mongodb 中不匹配，如何删除空文档？
【发布时间】：2019-07-31 18:09:54
【问题描述】：

如果 mongoDB 中的条件不匹配，请告诉我如何删除空文档

我在 shell 上试过这个查询

db.address.aggregate([
    { "$project": {
            "applications": {
                "$filter": {
                    "input": "$applications",
                    "as": "applications",
                    "cond": {
                        "$and": [
                            { "$eq": ["$$applications.name", "DSB"] },
                            { "$in": ["$$applications.code", ["122018"]] }
                        ]
                    }
                }
            }
        }}
])

我的收藏

[
  {
    "name": "test",
    "applications": [
      {
        "code": [
          "135001",
          "122017"
        ],
        "name": "HELLO"
      }
    ]
  },
  {
    "name": "test1",
    "applications": [
      {
        "name": "HELLO",
        "code": [
          "135001",
          "122017"
        ]
      }
    ]
  },
  {
    "name": "test2",
    "applications": [
      {
        "code": [
          "135001",
          "122017"
        ],
        "name": "HELLO"
      }
    ]
  },
  {
    "name": "test3",
    "applications": [
      {
        "code": [
          "135001",
          "122017"
        ],
        "name": "HELLO"
      }
    ]
  },
  {
    "name": "test4",
    "applications": [
      {
        "code": [
          "135001",
          "122017"
        ],
        "name": "HELLO"
      }
    ]
  },
  {
    "name": "test5",
    "applications": [
      {
        "code": [
          "135001",
          "122017"
        ],
        "name": "HELLO"
      }
    ]
  },
  {
    "name": "tes3",
    "applications": [
      {
        "code": [
        ],
        "name": "HELLO"
      }
    ]
  },
  {
    "name": "test22",
    "applications": [
      {
        "code": [
          "135001",
          "122017"
        ],
        "name": "DSB"
      }
    ]
  },
  {
    "name": "test89",
    "applications": [
      {
        "code": [
          "135001",
          "122017"
        ],
        "name": "DSB"
      },
      {
        "code": [
          "135001",
          "122017"
        ],
        "name": "HELLO"
      }
    ]
  },
  {
    "name": "test89",
    "applications": [
      {
        "code": [
          "135001",
          "122018"
        ],
        "name": "DSB"
      },
      {
        "code": [
          "135001",
          "122017"
        ],
        "name": "HELLO"
      }
    ]
  }
]

预期输出

   [
  {
    "name": "test89",
    "applications": [
      {
        "code": [
          "135001",
          "122018"
        ],
        "name": "DSB"
      }
    ]
  }
]

出去

{ "_id" : ObjectId("5d4143269d7b3f8883605a1e"), "applications" : [ ] }
{ "_id" : ObjectId("5d4143269d7b3f8883605a1f"), "applications" : [ ] }
{ "_id" : ObjectId("5d4143269d7b3f8883605a20"), "applications" : [ ] }
{ "_id" : ObjectId("5d4143269d7b3f8883605a21"), "applications" : [ ] }
{ "_id" : ObjectId("5d4143269d7b3f8883605a22"), "applications" : [ ] }
{ "_id" : ObjectId("5d4143269d7b3f8883605a23"), "applications" : [ ] }
{ "_id" : ObjectId("5d4143269d7b3f8883605a24"), "applications" : [ ] }
{ "_id" : ObjectId("5d4143269d7b3f8883605a25"), "applications" : [ ] }
{ "_id" : ObjectId("5d4143269d7b3f8883605a26"), "applications" : [ ] }
{ "_id" : ObjectId("5d4143269d7b3f8883605a27"), "applications" : [ ] }

请说明为什么我没有得到预期的输出？？

我想过滤我的集合，其中包含 application 名称“DSB”和代码 122018

查看我的预期输出，其中只有一个满足我条件的文档，名称为 DSB，代码为“122018”。

【问题讨论】：

标签： javascript mongodb mongoose mongodb-query

【解决方案1】：

您需要使用unwind 并且您的$in 条件中存在位置问题

db.address.aggregate([
    {
        "$project": {
            "applications": {
                "$filter": {
                    "input": "$applications",
                    "as": "applications",
                    "cond":  {
                        "$and": [
                            { "$in": ['122018',"$$applications.code"] },
                            { "$eq": ["$$applications.name", "DSB"] },
                        ]
                    }
                }
            },
            name:true
        }
    },
    { $unwind: { path: "$applications", preserveNullAndEmptyArrays: false } }
])

【讨论】：