需要从mongo db JSON返回匹配的数据

Question

我有Json，其值类似于state_city详细信息，其中包含诸如哪个城市属于哪个州的信息-

需要查询它的特定州名，这将为我提供属于该州的所有城市。

db.collection.find（{   “计数”：10，   “ state.name”：“ MP” }）

[
  {
    "collection": "collection1",
    "count": 10,
    "state": [
      {
        "name": "MH",
        "city": "Mumbai"
      },
      {
        "name": "MH",
        "city": "Pune"
      },
      {
        "name": "UP",
        "city": "Kanpur"
      },
      {
        "name": "CG",
        "city": "Raipur"
      }
    ]
  },
  {
    "collection": "collection2",
    "count": 20,
    "state": [
      {
        "name": "MP",
        "city": "Indore"
      },
      {
        "name": "MH",
        "city": "Bhopal"
      },
      {
        "name": "UP",
        "city": "Kanpur"
      },
      {
        "name": "CG",
        "city": "Raipur"
      }
    ]
  }
]

Answer 1

以下查询将是解决方案。

db.collection.find({ "count": 10, "state":{"name": "MP"}})

对于更复杂的查询，还可以使用 $ elemMatch 。

Answer 2

您必须使用聚合查询仅获取数组中匹配的元素：

db.collection.aggregate([{
    $unwind: "$content.state"
  },
  {
    $match: {
      "content.state.name": "MH",
      "count": 10
    }
  },
  {
    $group: {
      _id: "$content.state.city",
    }
  },
  {
    $addFields: {
      key: 1
    }
  },
  {
    $group: {
      _id: "$key",
      cities: {
        $push: "$_id"
      }
    }
  },
  {
    $project: {
      _id: 0,
      cities: 1
    }
  }
])

此查询将返回：

{
  "cities": [
    "Pune",
    "Mumbai"
  ]
}