使用元素匹配和过滤器执行pymongo查询。

Question

我有以下数据结构：

[
    {
        "site_id": ObjectId("5e85b9d20498abd407e9a030"),
        "status": "ERROR"
    },
    {
        "site_id": ObjectId("5e85b9d20498abd407e9a120"),
        "status": "ERROR"
    },
    {
        "site_id": ObjectId("5e85b9d20498abd407e9a030"),
        "status": "OK",
        "risk_categories": [
            {

                "position": 1,
                "category_id": 1414,
            },
            {

                "position": 2,
                "category_id": 1402,

            },
            {

                "position": 3,
                "category_id": 1392,

            }
                ]
    }
]

我想对pymongo进行如下查询：

collection.find_one(filter=filter)

其中: filter ={‘$’和‘：[{'$and'：{'site_id'：ObjectId('5e85b9d20498abd407e9a030')}，{“状态”：’OK‘}，{’危险_类别‘：{'$elemMatch'：{’$或‘：{’$‘{’eq‘：1}}，{’位置‘：{'$eq'：2}

但是，它会返回整个对象。不仅仅是我想要的风险类别的价值。我能在我的过滤器上做些什么来修改它？

Answer 1

聚合从mongo shell运行：

db.collection.aggregate( [
  { 
      $match:  { 
          site_id: ObjectId('5e85b9d20498abd407e9a030'), 
          status: "OK" 
      } 
  },
  { 
      $addFields: {
          risk_categories: { 
              $filter: { 
                  input: "$risk_categories", 
                  as: "cat",
                  cond: {
                      $in: [ "$$cat.position", [ 1, 2 ] ]    // this is equivalent to using the "$or"
                  }
              }
          }
      }
  },
] ).pretty()

产出：

{
        "_id" : ObjectId("5e85c7b6724e461876467077"),
        "site_id" : ObjectId("5e85b9d20498abd407e9a030"),
        "status" : "OK",
        "risk_categories" : [
                {
                        "position" : 1,
                        "category_id" : 1414
                },
                {
                        "position" : 2,
                        "category_id" : 1402
                }
        ]
}

使用Python中的PyMongo 3.9和MongoDB 4.2：

import pymongo
from pymongo import MongoClient
client = MongoClient()
db = client.test
collection = db.collection
import pprint
from bson.objectid import ObjectId

pipeline = [
  { 
      '$match':  { 
          'site_id': ObjectId('5e85b9d20498abd407e9a030'), 
          'status': 'OK'
      } 
  },
  { 
      '$addFields': {
          'risk_categories': { 
              '$filter': { 
                  'input': '$risk_categories', 
                  'as': 'cat',
                  'cond': {
                      '$in': [ '$$cat.position', [ 1, 2 ] ]
                  }
              }
          }
      }
  },
]

pprint.pprint(list(collection.aggregate(pipeline)))