Mongo filtering

gistfile1.txt

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp2.1</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Mongo2Go" Version="2.2.9" />
    <PackageReference Include="MongoDB.Driver" Version="2.8.0" />
  </ItemGroup>

</Project>

program.cs

using Mongo2Go;
using MongoDB.Bson.Serialization;
using MongoDB.Bson.Serialization.Attributes;
using MongoDB.Bson.Serialization.Serializers;
using MongoDB.Driver;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace MongoFiltering
{
    public class Program
    {
        public static async Task Main(string[] args)
        {
            var runner = MongoDbRunner.Start(singleNodeReplSet: true);
            var client = new MongoClient(runner.ConnectionString);
            var database = client.GetDatabase("testdb");
            var collection = database.GetCollection<Outer>(Guid.NewGuid().ToString());

            var elementId = Guid.NewGuid().ToString();
            var entry = new Outer
            {
                Id = Guid.NewGuid().ToString(),
                Value = 1,
                Elements = new List<Element>
                {
                    new Element { Id = elementId, Value = 1 }
                }
            };

            Console.WriteLine($"Entering data");
            await collection.InsertOneAsync(entry);

            Console.WriteLine($"Discovering data");
            await collection.FindAsync(x => x.Id == entry.Id);

            Console.WriteLine($"Updating outer data");
            await collection.FindOneAndUpdateAsync(x => x.Id == entry.Id, Builders<Outer>.Update.Set(x => x.Value, 5));

            Console.WriteLine($"Updating inner data");
            await collection.FindOneAndUpdateAsync(Builders<Outer>.Filter.Where(x => x.Elements.Any(e => e.Id == elementId)), Builders<Outer>.Update.Set(x => x.Elements[-1].Value, 5));

            Console.Read();
        }
    }

    public class Outer
    {
        public string Id { get; set; }
        public int Value { get; set; }

        [BsonSerializer(typeof(ElementsSerializer))]
        public List<Element> Elements { get; set; }
    }

    public class Element
    {
        public string Id { get; set; }
        public int Value { get; set; }
    }

    public class ElementsSerializer : EnumerableSerializerBase<List<Element>>
    {
        public override void Serialize(BsonSerializationContext context, BsonSerializationArgs args, List<Element> value) => base.Serialize(context, args, value);

        public override List<Element> Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args) => base.Deserialize(context, args);

        protected override void AddItem(object accumulator, object item) => ((List<Element>)accumulator).Add((Element)item);
        protected override object CreateAccumulator() => new List<Element>();
        protected override IEnumerable EnumerateItemsInSerializationOrder(List<Element> value) => value;
        protected override List<Element> FinalizeResult(object accumulator) => (List<Element>)accumulator;
    }
}