Mongodb 检查 collection 相同的参数

Question

我正在尝试检查 collection 是否有其他记录具有与 mongodb 聚合相同的参数。示例：

汽车collection:

[
  {
    "year": "2020",
    "model": "Opel"
  }, {
    "year": "2020",
    "model": "Renault"
  }, {
    "year": "2019",
    "model": "Renault"
  },
]

获取：按年份获取记录return：

[
   {
    "year": "2020",
    "model": "Opel"
  }, {
    "year": "2020",
    "model": "Renault"
  },
]

为每条记录添加变量 - "Does current record with name {name} has another record in this table - true / false"。预期结果：

[ 
  {
    "year": "2020",
    "model": "Opel",
    "hasAnotherRecord": false
  }, {
    "year": "2020",
    "model": "Renault",
    "hasAnotherRecord": true
  }
]

我怎样才能做到这一点？

Answer 1

不确定此管道的效率如何，但它 returns 您的预期输出：

db.cars.aggregate(
    [
        {
            "$group": {
                "_id": "$model",
                "cars": { "$push": { "model": "$model", "year": "$year" }}}
        },
        {
            "$project": {
                "cars": {
                    "$filter": {
                        "input": "$cars",
                        "as": "c",
                        "cond": { "$eq": [ "$$c.year", "2020" ]
                        }
                    }
                },
                "hasAnotherRecord": {
                    "$gt": [ { "$size": "$cars" }, 1 ]
                },
                "_id": 0
            }
        },
        {
            "$match": {
                "cars": {
                    "$ne": null,
                    "$not": { "$size": 0 }
                }
            }
        },
        {
            "$project": {
                "model": {
                    "$arrayElemAt": [ "$cars.model", 0 ]
                },
                "year": {
                    "$arrayElemAt": [ "$cars.year", 0 ]
                },
                "_id": 0
            }
        }
    ]
)

c#测试程序：

using MongoDB.Entities;
using MongoDB.Entities.Core;
using System.Linq;

namespace Whosebug
{
    public class car : Entity
    {
        public string year { get; set; }
        public string model { get; set; }
    }

    public static class Program
    {
        private static void Main()
        {
            new DB("test");

            new[] {
                new car { model= "opel", year= "2020"},
                new car { model= "renault", year= "2020"},
                new car { model= "renault", year= "2019"},
                new car { model= "nissan", year= "2021"}
            }.Save();

            var result = DB.Queryable<car>()
                           .GroupBy(c => c.model,
                                    (model, cars) => new
                                    {
                                        model,
                                        cars = cars.Select(c => new car
                                        {
                                            model = c.model,
                                            year = c.year
                                        })
                                    })
                           .Select(x => new
                           {
                               cars = x.cars.Where(c => c.year == "2020"),
                               hasAnotherRecord = x.cars.Count() > 1
                           })
                           .Where(x => x.cars.Any())
                           .Select(x => new
                           {
                               x.cars.First().model,
                               x.cars.First().year
                           })
                           .ToList();
        }
    }
}

Mongodb 检查 collection 相同的参数

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