如何使用 Linq 在带有字符串的集合上加入带有字符串 [] 的 MongoDB 集合

Question

我正在尝试加入两个集合。我设法将两者正确连接，其中连接部分的类型相同 - 但这不是目标。出现困难是因为我在其中一个集合中有一个字符串（id）列表，并且我想用另一个集合的对象替换该列表中的每个字符串，该对象是定义为的用户集合：

public string name { get; set; }
public string email { get; set; }
public string _id { get; set; }
public bool IsDeleted { get; set; }

我有两种类型的会议，我想将用户插入替换字符串的会议，因此它是 DTO。

public class MeetingBase : ModelBase
    {
        public string createdBy { get; set; }
        public string facilitator { get; set; }
        public string topic { get; set; }
        public string address { get; set; }
        public string city { get; set; }
        public string country { get; set; }
        public int RoomNumber { get; set; }
        public DateTime meetingDate { get; set; }

    }

public class Meeting : MeetingBase
    {
        public List<string> attendees { get; set; }
    }

public class MeetingDTO : MeetingBase
    {
        public List<User> attendees { get; set; }
    }

如前所述，我想将Meeting 的集合与users 的集合一起加入，从而得到MeetingDTO 的集合

到目前为止，我最好的尝试是这样的：

public async Task<List<MeetingDTO>> getMeetingDtos(string userid)
        {
            var userCollection = _userDataManager.GetDataContext().MongoCollection;
            var meetingCollection = _meetingDataManager.GetDataContext().MongoCollection;

            var query = from m in meetingCollection.AsQueryable()
                where (m.createdBy == userid)
                from attendee in m.attendees
                join u in userCollection.AsQueryable() on attendee equals u._id into meetingusers
                select new MeetingDTO()
                {
                    _id = m._id,
                    IsDeleted = m.IsDeleted,
                    attendees = meetingusers.ToList(),
                    address = m.address,
                    city = m.city,
                    country = m.country,
                    createdBy = m.createdBy,
                    facilitator = m.facilitator,
                    meetingDate = m.meetingDate,
                    RoomNumber = m.RoomNumber,
                    topic = m.topic

                };

            var result = query.ToList();
            return result;
        }

但是，这种尝试会产生以下运行时异常System.NotSupportedException: '$project or $group does not support {document}.'

Answer 1

您可以使用集合的.Aggregate() 接口来完成，如下所示：

    var meetingDTOs = meetingCollection.Aggregate()
                        .Match(m => m.createdBy == userid)
                        .Lookup<Meeting, User, MeetingDTO>(
                            userCollection,
                            m => m.attendees,
                            u => u.Id,
                            dto => dto.attendees)
                        .ToList();

测试程序：

using MongoDB.Bson;
using MongoDB.Bson.Serialization.Attributes;
using MongoDB.Driver;
using MongoDB.Entities;
using MongoDB.Entities.Core;
using System.Collections.Generic;
using System.Linq;

namespace StackOverFlow
{
    public class User : Entity
    {
        public string name { get; set; }
    }

    public class MeetingBase : Entity
    {
        public string createdBy { get; set; }
        public string topic { get; set; }
    }

    public class Meeting : MeetingBase
    {
        [BsonRepresentation(BsonType.ObjectId)]
        public List<string> attendees { get; set; }
    }

    public class MeetingDTO : MeetingBase
    {
        public List<User> attendees { get; set; }
    }

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

            var user1 = new User { name = "user one" };
            var user2 = new User { name = "user two" };
            new[] { user1, user2 }.Save();

            var meeting = new Meeting
            {
                attendees = new List<string> { user1.ID, user2.ID },
                createdBy = "god",
                topic = "corona beer"
            };
            meeting.Save();

            var meetingDTOs = DB.Fluent<Meeting>()
                                .Match(m => m.createdBy == "god")
                                .Lookup<Meeting, User, MeetingDTO>(
                                    DB.Collection<User>(),
                                    m => m.attendees,
                                    u => u.ID,
                                    dto => dto.attendees)
                                .ToList();
        }
    }
}