兼容SQLSERVER、Oracle、MYSQL、SQLITE的超级DBHelper

本示例代码的关键是利用.net库自带的DbProviderFactory来生产数据库操作对象。

从下图中，可以看到其的多个核心方法，这些方法将在我们的超级DBHelper中使用。

仔细研究，你会发现每个数据库的官方支持dll都有一个Instance对象，这个对象都是继承了DbProviderFactory了。

因此利用这点，我们就可以实现兼容多种数据的超级DBHelper了。

以下为示例代码,仅供参考学习，代码只是我的ORM框架中的一个片段（其中暂时支持了SQLSERVER、MySQL、SQLITE三种数据库，LoadDbProviderFactory方法是将封装在dll中的数据库操作dll反射加载实例化的方法。）：

     /// <summary>
     /// 超级数据库操作类
     /// <para>2015年12月21日</para>
     /// </summary>
     public class DBHelper
     {
         #region 属性
         private DbProviderFactory _DbFactory;
         private DBConfig mDBConfig;  

         /// <summary>
         /// 数据库连接配置
         /// </summary>
         public DBConfig DBConfig
         {
             get { return mDBConfig; }
         }  

         /// <summary>
         /// 表示一组方法，这些方法用于创建提供程序对数据源类的实现的实例。
         /// </summary>
         public DbProviderFactory DbFactory
         {
             get { return _DbFactory; }
             set { _DbFactory = value; }
         }
         #endregion  

         #region 构造函数
         public DBHelper(DBConfig aORMConfig)
         {
             mDBConfig = aORMConfig;
             switch (mDBConfig.DBType)
             {
                 case ORMType.DBTypes.SQLSERVER:
                     _DbFactory = System.Data.SqlClient.SqlClientFactory.Instance;
                     break;
                 case ORMType.DBTypes.MYSQL:
                     LoadDbProviderFactory("MySql.Data.dll", "MySql.Data.MySqlClient.MySqlClientFactory");
                     break;
                 case ORMType.DBTypes.SQLITE:
                     LoadDbProviderFactory("System.Data.SQLite.dll", "System.Data.SQLite.SQLiteFactory");
                     break;
             }
         }  

         /// <summary>
         /// 动态载入数据库封装库
         /// </summary>
         /// <param name="aDLLName">数据库封装库文件名称</param>
         /// <param name="aFactoryName">工厂路径名称</param>
         private void LoadDbProviderFactory(string aDLLName, string aFactoryName)
         {
             string dllPath = string.Empty;
             if (System.AppDomain.CurrentDomain.RelativeSearchPath != null)
             {
                 dllPath = System.AppDomain.CurrentDomain.RelativeSearchPath+"\\"+ aDLLName;
             }
             else
             {
                 dllPath = System.AppDomain.CurrentDomain.BaseDirectory + aDLLName;
             }
             if (!File.Exists(dllPath))
             {//文件不存在，从库资源中复制输出到基目录下
                 FileStream fdllFile = new FileStream(dllPath,FileMode.Create);
                 byte[] dllData = null;
                 if (aDLLName == "System.Data.SQLite.dll")
                 {
                     dllData = YFmk.ORM.Properties.Resources.System_Data_SQLite;
                 }
                 else if (aDLLName == "MySql.Data.dll")
                 {
                     dllData = YFmk.ORM.Properties.Resources.MySql_Data;
                 }
                 fdllFile.Write(dllData, , dllData.Length);
                 fdllFile.Close();
             }
             Assembly libAssembly = Assembly.LoadFile(dllPath);
             Type type = libAssembly.GetType(aFactoryName);
             foreach (FieldInfo fi in type.GetFields(BindingFlags.Static | BindingFlags.Public))
             {
                 if (fi.Name == "Instance")
                 {
                     _DbFactory = fi.GetValue(null) as DbProviderFactory;
                     return;
                 }
             }
         }
         #endregion  

         #region 数据库操作
         /// <summary>
         /// 执行一条计算查询结果语句，返回查询结果
         /// </summary>
         /// <param name="aSQLWithParameter">SQL语句及参数</param>
         /// <returns>查询结果（object）</returns>
         public object GetSingle(SQLWithParameter aSQLWithParameter)
         {
             using (DbConnection conn = _DbFactory.CreateConnection())
             {
                 conn.ConnectionString = mDBConfig.ConnString;
                 using (DbCommand cmd = _DbFactory.CreateCommand())
                 {
                     PrepareCommand(cmd, conn, aSQLWithParameter.SQL.ToString(), aSQLWithParameter.Parameters);
                     object obj = cmd.ExecuteScalar();
                     cmd.Parameters.Clear();
                     if ((Object.Equals(obj, null)) || (Object.Equals(obj, System.DBNull.Value)))
                     {
                         return null;
                     }
                     else
                     {
                         return obj;
                     }
                 }
             }
         }  

         /// <summary>
         /// 执行SQL语句，返回影响的记录数
         /// </summary>
         /// <param name="aSQL">SQL语句</param>
         /// <returns>影响的记录数</returns>
         public int ExecuteSql(string aSQL)
         {
             using (DbConnection conn = _DbFactory.CreateConnection())
             {
                 conn.ConnectionString = mDBConfig.ConnString;
                 using (DbCommand cmd = _DbFactory.CreateCommand())
                 {
                     PrepareCommand(cmd, conn, aSQL);
                     int rows = cmd.ExecuteNonQuery();
                     cmd.Parameters.Clear();
                     return rows;
                 }
             }
         }  

         /// <summary>
         /// 执行SQL语句，返回影响的记录数
         /// </summary>
         /// <param name="aSQLWithParameter">SQL语句及参数</param>
         /// <returns></returns>
         public int ExecuteSql(SQLWithParameter aSQLWithParameter)
         {
             using (DbConnection conn = _DbFactory.CreateConnection())
             {
                 conn.ConnectionString = mDBConfig.ConnString;
                 using (DbCommand cmd = _DbFactory.CreateCommand())
                 {
                     PrepareCommand(cmd, conn, aSQLWithParameter.SQL.ToString(), aSQLWithParameter.Parameters);
                     int rows = cmd.ExecuteNonQuery();
                     cmd.Parameters.Clear();
                     return rows;
                 }
             }
         }  

         /// <summary>
         /// 执行多条SQL语句，实现数据库事务。
         /// </summary>
         /// <param name="aSQLWithParameterList">参数化的SQL语句结构体对象集合</param>
         public string ExecuteSqlTran(List<SQLWithParameter> aSQLWithParameterList)
         {
             using (DbConnection conn = _DbFactory.CreateConnection())
             {
                 conn.ConnectionString = mDBConfig.ConnString;
                 conn.Open();
                 DbTransaction fSqlTransaction = conn.BeginTransaction();
                 try
                 {
                     List<DbCommand> fTranCmdList = new List<DbCommand>();
                     //创建新的CMD
                     DbCommand fFirstCMD = _DbFactory.CreateCommand();
                     fFirstCMD.Connection = conn;
                     fFirstCMD.Transaction = fSqlTransaction;
                     fTranCmdList.Add(fFirstCMD);
                     int NowCmdIndex = ;//当前执行的CMD索引值
                     int ExecuteCount = ;//已经执行的CMD次数
                     StringBuilder fSQL = new StringBuilder();
                     foreach (SQLWithParameter fSQLWithParameter in aSQLWithParameterList)
                     {
                         fSQL.Append(fSQLWithParameter.SQL.ToString() + ";");
                         fTranCmdList[NowCmdIndex].Parameters.AddRange(fSQLWithParameter.Parameters.ToArray());
                         if (fTranCmdList[NowCmdIndex].Parameters.Count > )
                         { //参数达到2000个，执行一次CMD
                             fTranCmdList[NowCmdIndex].CommandText = fSQL.ToString();
                             fTranCmdList[NowCmdIndex].ExecuteNonQuery();
                             DbCommand fNewCMD = _DbFactory.CreateCommand();
                             fNewCMD.Connection = conn;
                             fNewCMD.Transaction = fSqlTransaction;
                             fTranCmdList.Add(fNewCMD);
                             NowCmdIndex++;
                             ExecuteCount++;
                             fSQL.Clear();//清空SQL
                         }
                     }
                     if (ExecuteCount < fTranCmdList.Count)
                     {//已执行CMD次数小于总CMD数，执行最后一条CMD
                         fTranCmdList[fTranCmdList.Count - ].CommandText = fSQL.ToString();
                         fTranCmdList[fTranCmdList.Count - ].ExecuteNonQuery();
                     }
                     fSqlTransaction.Commit();
                     return null;
                 }
                 catch (Exception ex)
                 {
                     fSqlTransaction.Rollback();
                     StringBuilder fSQL = new StringBuilder();
                     foreach (SQLWithParameter fSQLWithParameter in aSQLWithParameterList)
                     {
                         fSQL.Append(fSQLWithParameter.SQL.ToString() + ";");
                     }
                     YFmk.Lib.LocalLog.WriteByDate(fSQL.ToString()+" 错误："+ex.Message, "ORM");
                     return ex.Message;
                 }
             }
         }  

         /// <summary>
         /// 执行查询语句，返回DataSet
         /// </summary>
         /// <param name="SQLString">查询语句</param>
         /// <returns>DataSet</returns>
         public DataSet Query(string SQLString)
         {
             using (DbConnection conn = _DbFactory.CreateConnection())
             {
                 conn.ConnectionString = mDBConfig.ConnString;
                 using (DbCommand cmd = _DbFactory.CreateCommand())
                 {
                     PrepareCommand(cmd, conn, SQLString);
                     using (DbDataAdapter da = _DbFactory.CreateDataAdapter())
                     {
                         da.SelectCommand = cmd;
                         DataSet ds = new DataSet();
                         try
                         {
                             da.Fill(ds, "ds");
                             cmd.Parameters.Clear();
                         }
                         catch (Exception ex)
                         {  

                         }
                         return ds;
                     }
                 }
             }
         }  

         /// <summary>
         /// 执行查询语句，返回DataSet
         /// </summary>
         /// <param name="aSQLWithParameter">查询语句</param>
         /// <returns>DataSet</returns>
         public DataSet Query(SQLWithParameter aSQLWithParameter)
         {
             using (DbConnection conn = _DbFactory.CreateConnection())
             {
                 conn.ConnectionString = mDBConfig.ConnString;
                 using (DbCommand cmd = _DbFactory.CreateCommand())
                 {
                     PrepareCommand(cmd, conn, aSQLWithParameter.SQL.ToString(), aSQLWithParameter.Parameters);
                     using (DbDataAdapter da = _DbFactory.CreateDataAdapter())
                     {
                         da.SelectCommand = cmd;
                         DataSet ds = new DataSet();
                         da.Fill(ds, "ds");
                         cmd.Parameters.Clear();
                         return ds;
                     }
                 }
             }
         }
         #endregion  

         #region 私有函数
         private void PrepareCommand(DbCommand cmd, DbConnection conn, string cmdText)
         {
             if (conn.State != ConnectionState.Open)
                 conn.Open();
             cmd.Connection = conn;
             cmd.CommandText = cmdText;
         }  

         private void PrepareCommand(DbCommand cmd, DbConnection conn, string cmdText, List<DbParameter> cmdParms)
         {
             if (conn.State != ConnectionState.Open)
                 conn.Open();
             cmd.Connection = conn;
             cmd.CommandText = cmdText;
             if (cmdParms != null && cmdParms.Count>)
             {
                 cmd.Parameters.AddRange(cmdParms.ToArray());
             }
         }
         #endregion