MongoDB - 查找查询中嵌套对象的投影

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。我尝试了以下查找查询：

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

我收到一个错误，因为无法将字段

meta.region

包含在排除投影中。 还有其他方法可以解决这个问题吗？ 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"
})

Mongo 游乐场示例