using System;
using System.Buffers;
using System.Buffers.Text;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;
using MongoDB.Bson;
using MongoDB.Driver;

namespace TestApplication
{
    class Program
    {
        static async Task Main(string[] args)
        {
            var client = new MongoClient("mongodb://127.0.0.1:27017");

            var database = client.GetDatabase("TestDb");

            using (var session = await client.StartSessionAsync())
            {
                session.StartTransaction();

                await Task.WhenAll(
                    WriteA(database, session),
                    WriteB(database, session)
                );

                await session.CommitTransactionAsync();
            }
            
            Console.Read();
        }

        private static Task WriteA(IMongoDatabase db, IClientSessionHandle session)
        {
           return db.GetCollection<CollectionAEntity>("CollectionA").InsertOneAsync(session, new CollectionAEntity
           {
               Name = "SomeStringA"
           });
        }

        private static Task WriteB(IMongoDatabase db, IClientSessionHandle session)
        {
            return db.GetCollection<CollectionBEntity>("CollectionB").InsertOneAsync(session, new CollectionBEntity
            {
                Name = "SomeStringB"
            });
        }
    }

    public class CollectionAEntity
    {
        public ObjectId Id { get; set; }
        
        public string Name { get; set; }
    }
    
    public class CollectionBEntity
    {
        public ObjectId Id { get; set; }
        
        public string Name { get; set; }
    }
}