MongoDb Projection Writer

MongoDbProjectionWriter.cs

using System;
using MongoDB.Bson;
using MongoDB.Driver;
using MongoDB.Driver.Builders;

namespace Recipes.ReadModel
{
    public class MongoDbProjectionWriter<T> : IProjectionWriter<T>
        where T: class
    {
        private const string DATABASE_NAME = "Recipes";
        private readonly string connectionString;
        private static MongoCollection<T> _collection;

        public MongoDbProjectionWriter(string connectionString)
        {
            this.connectionString = connectionString;
        }

        public void Add(int id, T item)
        {
            var collection = GetCollection();
            collection.Insert(item);
        }

        public void Update(int id, Action<T> update)
        {
            var query = Query.EQ("_id", new BsonInt32(id));
            var collection = GetCollection();
            var existingItem = collection.FindOneAs<T>(query);

            if (existingItem == null)
                throw new InvalidOperationException("Item does not exists");

            update(existingItem);
            collection.Save(existingItem);
        }

        private MongoCollection<T> GetCollection()
        {
            if (_collection == null)
            {
                var client = new MongoClient(connectionString);
                var server = client.GetServer();
                var database = server.GetDatabase(DATABASE_NAME);
                _collection = database.GetCollection<T>(typeof(T).Name);
            }
            return _collection;
        }
    }
}