工厂模式的数据库连接

 /// 数据连接字符串
        /// </summary>
        private static string connectionString;
        /// <summary>
        /// 数据库 驱动 提供者
        /// </summary>
        private static string providerName;
        /// <summary>
        /// 数据库 驱动 提供者 工厂
        /// </summary>
        private static DbProviderFactory factory;

        static Database()
        {
            ConnectionStringSettings settings = ConfigurationManager.ConnectionStrings["default"];
            connectionString = settings.ConnectionString;
            providerName = settings.ProviderName;
            factory = DbProviderFactories.GetFactory(providerName);
        }