using MongoDB.Bson.Serialization;
using MongoDB.Driver;
 
namespace MongoCounterDemo
{
    class Program
    {
        private const string ConnectionString = "mongodb://user:password@host:27017/database";
 
        static void Main(string[] args)
        {
            var customerCounter = new MongoDbCounter(ConnectionString, "Customers");
            customerCounter.GetNextNumber();
        }
    }
 
    class MongoDbCounter
    {
        #region Constants
 
        private const string CounterCollectionName = "Counters";
 
        #endregion
 
        #region Fields
 
        private readonly string _connectionString;
        private readonly string _counterName;
 
        #endregion
 
        #region Constructor
 
        public MongoDbCounter(string connectionString, string counterName)
        {
            _connectionString = connectionString;
            _counterName = counterName;
        }
 
        #endregion
 
        #region Public Methods
 
        public int GetNextNumber()
        {
            var client = new MongoClient(_connectionString);
            var databaseName = new MongoUrl(_connectionString).DatabaseName;
            var db = client.GetDatabase(databaseName);
            var counterCol = db.GetCollection<Counter>(CounterCollectionName); 
            var filter2 = Builders<Counter>.Filter.Eq("_id", _counterName);
            var update2 = Builders<Counter>.Update.Inc(c => c.Value, 1);
            var options2 = new FindOneAndUpdateOptions<Counter> { IsUpsert = true, ReturnDocument = ReturnDocument.After};
            var result2 = counterCol.FindOneAndUpdate(filter2, update2, options2);
 
            return result2.Value;
        }
 
        #endregion
    }
 
    class Counter
    {
        static Counter()
        {
            BsonClassMap.RegisterClassMap<Counter>(cm =>
            {
                cm.MapIdMember(c => c.Id);
                cm.MapProperty(c => c.Value);
            });
        }
 
        public string Id { get; set; }
        public int Value { get; set; }
    }
}