1.直接黏貼代碼

public sealed class DaoHelper {
        private static DataTable _providers = null;
        private DbProviderFactory _pf = null;

        /// <summary>
        /// 靜態(tài)構(gòu)造函數(shù)，初始化數(shù)據(jù)提供程序列表。
        /// </summary>
        static DaoHelper() {
            _providers = DbProviderFactories.GetFactoryClasses();
        }
        /// <summary>
        /// 初始化 DAOHelper 類的新實(shí)例。
        /// </summary>
        public DaoHelper() {
        }
        /// <summary>
        /// 用指定的數(shù)據(jù)提供程序名稱，初始化 DAOHelper 類的新實(shí)例。
        /// </summary>
        /// <param name="providerName">數(shù)據(jù)提供程序名稱。</param>
        public DaoHelper(string providerName) {
            this.ProviderName = providerName;
        }

        private string m_providerName = "";

        /// <summary>
        /// 獲取或設(shè)置數(shù)據(jù)提供程序名稱。
        /// </summary>
        public string ProviderName {
            get { return m_providerName; }
            set {
                if(string.IsNullOrEmpty(value)){
                    throw new ArgumentNullException("value");
                }

                if(m_providerName != value) {
                    ChangeProvider(value);
                }
            }
        }

        /// <summary>
        /// 查找指定數(shù)名稱的據(jù)提供程序行。
        /// </summary>
        /// <param name="providerInvariantName">數(shù)據(jù)提供程序名稱。</param>
        /// <returns></returns>
        private DataRow FindProviderRow(string providerInvariantName) {
            if(_providers != null) {
                return _providers.Rows.Find(providerInvariantName);
            }
            throw new ProvidersNotFoundException();
        }

        /// <summary>
        /// 根據(jù)參數(shù)提供的數(shù)據(jù)提供程序名稱，更改當(dāng)前的數(shù)據(jù)提供程序工廠。
        /// </summary>
        /// <param name="providerName">數(shù)據(jù)提供程序名稱。</param>
        private void ChangeProvider(string providerName) {
            if(string.IsNullOrEmpty(providerName)) {
                throw new ArgumentNullException("value");
            }

            DataRow providerRow = FindProviderRow(providerName);
            if(providerRow == null){
                throw new ProviderNotFoundException(providerName);              
            }
            _pf = DbProviderFactories.GetFactory(providerRow);
            m_providerName = providerName;
            
        }

        /// <summary>
        /// 創(chuàng)建數(shù)據(jù)源枚舉器。
        /// </summary>
        /// <returns>返回創(chuàng)建成功的數(shù)據(jù)源枚舉器。</returns>
        public DbDataSourceEnumerator CreateDataSourceEnumerator() {
            if(_pf == null) {
                throw new ProviderFactoryNullException();
            }
            return _pf.CreateDataSourceEnumerator();
        }

        /// <summary>
        /// 創(chuàng)建數(shù)據(jù)庫(kù)連接。
        /// </summary>
        /// <returns>返回成功創(chuàng)建的連接對(duì)象。</returns>
        public DbConnection CreateConnection() {
            if(_pf == null) {
                throw new ProviderFactoryNullException();
            }
            return _pf.CreateConnection();
        }

        /// <summary>
        /// 創(chuàng)建數(shù)據(jù)庫(kù)連接，并用指定的數(shù)據(jù)庫(kù)連接字符串打開(kāi)。
        /// </summary>
        /// <param name="connectionString">數(shù)據(jù)庫(kù)連接字符串。</param>
        /// <returns>返回成功創(chuàng)建并打開(kāi)的連接對(duì)象。</returns>
        public DbConnection CreateConnection(string connectionString){
            DbConnection result = CreateConnection();
            result.ConnectionString = connectionString;
            result.Open();
            return result;
        }

        /// <summary>
        /// 創(chuàng)建數(shù)據(jù)庫(kù)連接字符串生成器。
        /// </summary>
        /// <returns>返回成功創(chuàng)建的連接對(duì)象。</returns>
        public DbConnectionStringBuilder CreateConnectionStringBuilder() {
            if(_pf == null) {
                throw new ProviderFactoryNullException();
            }
            return _pf.CreateConnectionStringBuilder();
        }

        /// <summary>
        /// 創(chuàng)建數(shù)據(jù)適配器。
        /// </summary>
        /// <returns></returns>
        public DataAdapter CreateAdapter() {
            if(_pf == null) {
                throw new ProviderFactoryNullException();
            }
            return _pf.CreateDataAdapter();
        }
    }