嵌套对象上的投影 mongodb 查找查询

Question

如何在 mongodb 查找查询中获取投影中的嵌套对象。

[
  {
    "apikey": 1,
    "meta": {
      "region": {
        "country": "India",
        "city": "bangalore",
        "pincode": 560067
      },
      "address": {
        "houseNo": "G/C 42 Whitefield boulavourd",
        "landmark": "whitefield boulavourd"
      }
    }
  },
  {
    "apikey": 2,
    "meta": {
      "region": {
        "country": "Germaany",
        "city": "Munich",
        "pincode": 80297
      },
      "address": {
        "houseNo": "Zweibrückenstraße 12",
        "landmark": "Zweibrückenstraße 12"
      }
    }
  }
]

我试图获取 apikey 2 的区域。我在下面尝试查找查询我尝试查找查询，即

db.collection.find({
    "apikey": "2"
  },
  {
    "projection": {
      "_id": 0,
      "apikey": 1,
      "meta.region": 1
    }
})

我收到错误消息，关于无法在排除投影中对字段 meta.region 进行包含。有没有其他方法可以解决这个问题。我想要输出，

[
    {
        "apikey":2,
        "region": {
            "country": "Germaany",
            "city": "Munich",
            "pincode": 80297
        }
    }
]

这是mongoplayground

Answer 1

删除 projection（环绕）级别。

db.collection.find({
  apikey: 2
},
{
  "_id": 1,
  "apikey": "$apikey",
  "region": "$meta.region"
})

Sample Mongo Playground

嵌套对象上的投影 mongodb 查找查询

Projection on nested object mongodb find query

mongodb

find

projection

nested-object