使用 mongoDB 和 pymongo 在嵌套字典中查询 arrays

Question

I have a dictionary like this:

dici = {
  "city": {
    "coord": {
      "lat": 123123123,
      "lon": 123123
    },
    "country": "asdsd",
    "id": 2735943,
    "name": "qweqwe",
    "population": 249633,
    "sunrise": 1617689349,
    "sunset": 1617735844,
    "timezone": 3600
  },
  "cnt": 40,
  "cod": "200",
  "list": [
    {
      "clouds": {
        "all": 0
      },
      "dt": 1617721200,
      "dt_txt": "2021-04-06 15:00:00",
      "main": {
        "feels_like": 17.87,
        "grnd_level": 1002,
        "humidity": 65,
        "pressure": 1014,
        "sea_level": 1014,
        "temp": 18.29,
        "temp_kf": 0.25,
        "temp_max": 18.29,
        "temp_min": 18.04
      },
      "pop": 0,
      "sys": {
        "pod": "d"
      },
      "visibility": 10000,
      "weather": [
        {
          "description": "clear sky",
          "icon": "01d",
          "id": 800,
          "main": "Clear"
        }
      ],
      "wind": {
        "deg": 299,
        "speed": 3.36
      }
    },
    {
      "clouds": {
        "all": 16
      },
      "dt": 1617732000,
      "dt_txt": "2021-04-06 18:00:00",
      "main": {
        "feels_like": 15.78,
        "grnd_level": 1001,
        "humidity": 63,
        "pressure": 1013,
        "sea_level": 1013,
        "temp": 16.44,
        "temp_kf": 0.58,
        "temp_max": 16.44,
        "temp_min": 15.86
      },
      "pop": 0,
      "sys": {
        "pod": "d"
      },
      "visibility": 10000,
      "weather": [
        {
          "description": "few clouds",
          "icon": "02d",
          "id": 801,
          "main": "Clouds"
        }
      ],
      "wind": {
        "deg": 295,
        "speed": 2.21
      }
    }
  ]
}`

And I would like to extract the entries of the array list when for example temp_max is greater than 16. What I have been doing is the following:

    unwind = db.forecast.aggregate([
    {"$unwind": "$list"},
    {"$project":{"list.dt_txt":1,
                 "list.main.temp":1,
                "list.main.temp_max":1,
                "list.main.temp_min":1}},
    {"$match":{"list.main.temp_max":{"$gt":10}}
     }
])

a = db.forecast.aggregate([
    {"$match":
         {"list.main[*].temp_max": {"$gt": 10}}}
])


b = db.forecast.find({"list.main.temp_max":{"$gt":16}})

But all of them get errors in the syntax, I can't seem to find the right syntax to access the temp_max key. Anyone can help me? Thanks!

Answer 1

You were close with the first query; this should work:

unwind = db.forecast.aggregate([
    {"$unwind": "$list"},
    {"$match": {"list.main.temp_max": {"$gt": 16}}},
    {"$project": {"list.dt_txt": 1, "list.main.temp": 1,
                  "list.main.temp_max": 1, "list.main.temp_min": 1, '_id': 0}}
])

Alternatively a find would work but only matches on the first list item, so the aggregate query is likely better.

b = db.forecast.find({"list.main.temp_max": {"$gt": 16}}, {'list.main.$': 1, '_id': 0})