Как выбрать запись из массива в коллекции MongoDB

Question

Я новичок в MongoDB.

Просто создал коллекцию с именем datasets и вставил в нее один большой json.

Документ:

{
   "_id":ObjectId(   "5e1f2b248eebbe6d289d53c6"   ),
   "countries":{
      "country":[
         {
            "area":9596960,
            "cities":{
               "city":[
                  {
                     "citypopulation":7830000,
                     "cityname":"Shanghai"
                  },
                  {
                     "citypopulation":7000000,
                     "cityname":"Beijing"
                  },
                  {
                     "citypopulation":6218000,
                     "cityname":"HongKong"
                  },
                  {
                     "citypopulation":5770000,
                     "cityname":"Tianjin"
                  },
                  {
                     "citypopulation":4540000,
                     "cityname":"Shenyang"
                  },
                  {
                     "citypopulation":3750000,
                     "cityname":"Wuhan"
                  },
                  {
                     "citypopulation":3580000,
                     "cityname":"Guangzhou"
                  },
                  {
                     "citypopulation":2980000,
                     "cityname":"Chongqing"
                  },
                  {
                     "citypopulation":2830000,
                     "cityname":"Harbin"
                  },
                  {
                     "citypopulation":2810000,
                     "cityname":"Chengdu"
                  },
                  {
                     "citypopulation":2760000,
                     "cityname":"Xian"
                  },
                  {
                     "citypopulation":2500000,
                     "cityname":"Nanjing"
                  },
                  {
                     "citypopulation":2460000,
                     "cityname":"Zibo"
                  },
                  {
                     "citypopulation":2400000,
                     "cityname":"Dalian"
                  },
                  {
                     "citypopulation":2320000,
                     "cityname":"Jinan"
                  },
                  {
                     "citypopulation":2110000,
                     "cityname":"Changchun"
                  },
                  {
                     "citypopulation":2060000,
                     "cityname":"Qingdao"
                  },
                  {
                     "citypopulation":1960000,
                     "cityname":"Taiyuan"
                  },
                  {
                     "citypopulation":1710000,
                     "cityname":"Zhengzhou"
                  },
                  {
                     "citypopulation":1530000,
                     "cityname":"Guiyang"
                  },
                  {
                     "citypopulation":1520000,
                     "cityname":"Kunming"
                  },
                  {
                     "citypopulation":1510000,
                     "cityname":"Lanzhou"
                  },
                  {
                     "citypopulation":1500000,
                     "cityname":"Tangshan"
                  },
                  {
                     "citypopulation":1390000,
                     "cityname":"Anshan"
                  },
                  {
                     "citypopulation":1380000,
                     "cityname":"Qiqihar"
                  },
                  {
                     "citypopulation":1350000,
                     "cityname":"Nanchang"
                  },
                  {
                     "citypopulation":1350000,
                     "cityname":"Fushun"
                  },
                  {
                     "citypopulation":1340000,
                     "cityname":"Hangzhou"
                  },
                  {
                     "citypopulation":1330000,
                     "cityname":"Changsha"
                  },
                  {
                     "citypopulation":1320000,
                     "cityname":"Shijiazhuang"
                  },
                  {
                     "citypopulation":1290000,
                     "cityname":"Fuzhou"
                  },
                  {
                     "citypopulation":1270000,
                     "cityname":"Jilin"
                  },
                  {
                     "citypopulation":1200000,
                     "cityname":"Huainan"
                  },
                  {
                     "citypopulation":1200000,
                     "cityname":"Baotou"
                  },
                  {
                     "citypopulation":1190000,
                     "cityname":"Luoyang"
                  },
                  {
                     "citypopulation":1160000,
                     "cityname":"Urumqi"
                  },
                  {
                     "citypopulation":1110000,
                     "cityname":"Handan"
                  },
                  {
                     "citypopulation":1110000,
                     "cityname":"Datong"
                  },
                  {
                     "citypopulation":1090000,
                     "cityname":"Ningbo"
                  },
                  {
                     "citypopulation":1070000,
                     "cityname":"Nanning"
                  },
                  {
                     "citypopulation":1000000,
                     "cityname":"Hefei"
                  }
               ]
            },
            "name":"China",
            "population":1210004992
         },
         {
            "area":3287590,
            "cities":{
               "city":[
                  {
                     "citypopulation":9925891,
                     "cityname":"Mumbai"
                  },
                  {
                     "citypopulation":7206704,
                     "cityname":"NewDelhi"
                  },
                  {
                     "citypopulation":4399819,
                     "cityname":"Calcutta"
                  },
                  {
                     "citypopulation":3841396,
                     "cityname":"Madras"
                  },
                  {
                     "citypopulation":3302296,
                     "cityname":"Bangalore"
                  },
                  {
                     "citypopulation":3145939,
                     "cityname":"Hyderabad"
                  },
                  {
                     "citypopulation":2954526,
                     "cityname":"Ahmadabad"
                  },
                  {
                     "citypopulation":1879420,
                     "cityname":"Kanpur"
                  },
                  {
                     "citypopulation":1624752,
                     "cityname":"Nagpur"
                  },
                  {
                     "citypopulation":1619115,
                     "cityname":"Lucknow"
                  },
                  {
                     "citypopulation":1566651,
                     "cityname":"Pune"
                  },
                  {
                     "citypopulation":1505872,
                     "cityname":"Surat"
                  },
                  {
                     "citypopulation":1458183,
                     "cityname":"Jaipur"
                  },
                  {
                     "citypopulation":1091674,
                     "cityname":"Indore"
                  },
                  {
                     "citypopulation":1062771,
                     "cityname":"Bhopal"
                  },
                  {
                     "citypopulation":1061598,
                     "cityname":"Vadodara"
                  },
                  {
                     "citypopulation":1042740,
                     "cityname":"Ludhiana"
                  },
                  {
                     "citypopulation":1014557,
                     "cityname":"Kalyan"
                  }
               ]
            },
            "name":"India",
            "population":952107712
         }
      ]
   }
}

Я хочу знать, какие типы операций поиска я могу сделать, чтобы выбрать эту json запись для целей обучения ..?

Я пытался запустить ниже операцию поиска, в результате ничего не получается.

db.datasets.find({'name':'China'})

Во-вторых, я добавил выше json в datasets коллекциях, используя следующую команду

mongoimport --db admin --collection datasets --file /home/lenny/TransformedJSON.json

Работает нормально, но я хочу не выполнить эту команду. Потому что я не хочу вставлять без имени пользователя и пароля. Как это можно сделать?

Кто-нибудь может подсказать, пожалуйста ..?

Answer 1

Оператор $ elemMatch используется для фильтрации значений в массиве.

db.getCollection("datasets").find({
        'countries.country': {
            $elemMatch: {
                name: 'China'
            }
        }
    }, {
        'countries.country.$': 1
    })

Answer 2

Ошибка с .find() :

db.datasets.find({ 'countries.country.name': 'China' },
    { "countries.country.$": 1 })

Из вышеприведенного поля name не на уровне документа, вы не можете напрямую запрашивать его поле, так как оно вложено, вам нужно использовать нотацию ., чтобы добраться до этой точки. Более того, поскольку он находится в массиве, вам нужно получить заданный элемент из массива countries.country, который соответствует фильтру, поэтому мы используем позиционный оператор, подробнее здесь: позиционная проекция

Средство для аутентификации:

Я подозреваю, что вы, возможно, работаете с mongoDB, размещенным в вашей локальной сети, тогда вам нужно создать пользователя для этого экземпляра, попытаться проверить его официальную документацию здесь :: db.createUser () - local-database , create-users

Результат:

/* 1 */
{
    "_id" : ObjectId("5e1f2b248eebbe6d289d53c6"),
    "countries" : {
        "country" : [ 
            {
                "area" : 9596960,
                "cities" : {
                    "city" : [ 
                        {
                            "citypopulation" : 7830000,
                            "cityname" : "Shanghai"
                        }, 
                        {
                            "citypopulation" : 7000000,
                            "cityname" : "Beijing"
                        }, 
                        {
                            "citypopulation" : 6218000,
                            "cityname" : "HongKong"
                        }, 
                        {
                            "citypopulation" : 5770000,
                            "cityname" : "Tianjin"
                        }, 
                        {
                            "citypopulation" : 4540000,
                            "cityname" : "Shenyang"
                        }, 
                        {
                            "citypopulation" : 3750000,
                            "cityname" : "Wuhan"
                        }, 
                        {
                            "citypopulation" : 3580000,
                            "cityname" : "Guangzhou"
                        }, 
                        {
                            "citypopulation" : 2980000,
                            "cityname" : "Chongqing"
                        }, 
                        {
                            "citypopulation" : 2830000,
                            "cityname" : "Harbin"
                        }, 
                        {
                            "citypopulation" : 2810000,
                            "cityname" : "Chengdu"
                        }, 
                        {
                            "citypopulation" : 2760000,
                            "cityname" : "Xian"
                        }, 
                        {
                            "citypopulation" : 2500000,
                            "cityname" : "Nanjing"
                        }, 
                        {
                            "citypopulation" : 2460000,
                            "cityname" : "Zibo"
                        }, 
                        {
                            "citypopulation" : 2400000,
                            "cityname" : "Dalian"
                        }, 
                        {
                            "citypopulation" : 2320000,
                            "cityname" : "Jinan"
                        }, 
                        {
                            "citypopulation" : 2110000,
                            "cityname" : "Changchun"
                        }, 
                        {
                            "citypopulation" : 2060000,
                            "cityname" : "Qingdao"
                        }, 
                        {
                            "citypopulation" : 1960000,
                            "cityname" : "Taiyuan"
                        }, 
                        {
                            "citypopulation" : 1710000,
                            "cityname" : "Zhengzhou"
                        }, 
                        {
                            "citypopulation" : 1530000,
                            "cityname" : "Guiyang"
                        }, 
                        {
                            "citypopulation" : 1520000,
                            "cityname" : "Kunming"
                        }, 
                        {
                            "citypopulation" : 1510000,
                            "cityname" : "Lanzhou"
                        }, 
                        {
                            "citypopulation" : 1500000,
                            "cityname" : "Tangshan"
                        }, 
                        {
                            "citypopulation" : 1390000,
                            "cityname" : "Anshan"
                        }, 
                        {
                            "citypopulation" : 1380000,
                            "cityname" : "Qiqihar"
                        }, 
                        {
                            "citypopulation" : 1350000,
                            "cityname" : "Nanchang"
                        }, 
                        {
                            "citypopulation" : 1350000,
                            "cityname" : "Fushun"
                        }, 
                        {
                            "citypopulation" : 1340000,
                            "cityname" : "Hangzhou"
                        }, 
                        {
                            "citypopulation" : 1330000,
                            "cityname" : "Changsha"
                        }, 
                        {
                            "citypopulation" : 1320000,
                            "cityname" : "Shijiazhuang"
                        }, 
                        {
                            "citypopulation" : 1290000,
                            "cityname" : "Fuzhou"
                        }, 
                        {
                            "citypopulation" : 1270000,
                            "cityname" : "Jilin"
                        }, 
                        {
                            "citypopulation" : 1200000,
                            "cityname" : "Huainan"
                        }, 
                        {
                            "citypopulation" : 1200000,
                            "cityname" : "Baotou"
                        }, 
                        {
                            "citypopulation" : 1190000,
                            "cityname" : "Luoyang"
                        }, 
                        {
                            "citypopulation" : 1160000,
                            "cityname" : "Urumqi"
                        }, 
                        {
                            "citypopulation" : 1110000,
                            "cityname" : "Handan"
                        }, 
                        {
                            "citypopulation" : 1110000,
                            "cityname" : "Datong"
                        }, 
                        {
                            "citypopulation" : 1090000,
                            "cityname" : "Ningbo"
                        }, 
                        {
                            "citypopulation" : 1070000,
                            "cityname" : "Nanning"
                        }, 
                        {
                            "citypopulation" : 1000000,
                            "cityname" : "Hefei"
                        }
                    ]
                },
                "name" : "China",
                "population" : 1210004992
            }
        ]
    }
}