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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。）：
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/// <summary>
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/// 超级数据库操作类
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/// <para>2015年12月21日</para>
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/// <para>v1.0</para>
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/// <para>叶琪</para>
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/// </summary>
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public class DBHelper
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{
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#region 属性
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private DbProviderFactory _DbFactory;
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private DBConfig mDBConfig;
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/// <summary>
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/// 数据库连接配置
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/// </summary>
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public DBConfig DBConfig
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{
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get { return mDBConfig; }
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}
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/// <summary>
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/// 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。
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/// </summary>
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public DbProviderFactory DbFactory
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{
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get { return _DbFactory; }
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set { _DbFactory = value; }
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}
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#endregion
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#region 构造函数
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public DBHelper(DBConfig aORMConfig)
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{
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mDBConfig = aORMConfig;
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switch (mDBConfig.DBType)
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{
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case ORMType.DBTypes.SQLSERVER:
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_DbFactory = System.Data.SqlClient.SqlClientFactory.Instance;
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break;
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case ORMType.DBTypes.MYSQL:
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LoadDbProviderFactory("MySql.Data.dll", "MySql.Data.MySqlClient.MySqlClientFactory");
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break;
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case ORMType.DBTypes.SQLITE:
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LoadDbProviderFactory("System.Data.SQLite.dll", "System.Data.SQLite.SQLiteFactory");
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break;
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}
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}
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/// <summary>
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/// 动态载入数据库封装库
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/// </summary>
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/// <param name="aDLLName">数据库封装库文件名称</param>
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/// <param name="aFactoryName">工厂路径名称</param>
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private void LoadDbProviderFactory(string aDLLName, string aFactoryName)
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{
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string dllPath = string.Empty;
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if (System.AppDomain.CurrentDomain.RelativeSearchPath != null)
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{
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dllPath = System.AppDomain.CurrentDomain.RelativeSearchPath+"\\"+ aDLLName;
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}
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else
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{
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dllPath = System.AppDomain.CurrentDomain.BaseDirectory + aDLLName;
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}
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if (!File.Exists(dllPath))
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{//文件不存在，从库资源中复制输出到基目录下
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FileStream fdllFile = new FileStream(dllPath,FileMode.Create);
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byte[] dllData = null;
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if (aDLLName == "System.Data.SQLite.dll")
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{
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dllData = YFmk.ORM.Properties.Resources.System_Data_SQLite;
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}
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else if (aDLLName == "MySql.Data.dll")
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{
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dllData = YFmk.ORM.Properties.Resources.MySql_Data;
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}
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fdllFile.Write(dllData, 0, dllData.Length);
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fdllFile.Close();
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}
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Assembly libAssembly = Assembly.LoadFile(dllPath);
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Type type = libAssembly.GetType(aFactoryName);
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foreach (FieldInfo fi in type.GetFields(BindingFlags.Static | BindingFlags.Public))
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{
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if (fi.Name == "Instance")
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{
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_DbFactory = fi.GetValue(null) as DbProviderFactory;
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return;
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}
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}
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}
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#endregion
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#region 数据库操作
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/// <summary>
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/// 执行一条计算查询结果语句，返回查询结果
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/// </summary>
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/// <param name="aSQLWithParameter">SQL语句及参数</param>
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/// <returns>查询结果（object）</returns>
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public object GetSingle(SQLWithParameter aSQLWithParameter)
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{
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using (DbConnection conn = _DbFactory.CreateConnection())
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{
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conn.ConnectionString = mDBConfig.ConnString;
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using (DbCommand cmd = _DbFactory.CreateCommand())
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{
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PrepareCommand(cmd, conn, aSQLWithParameter.SQL.ToString(), aSQLWithParameter.Parameters);
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object obj = cmd.ExecuteScalar();
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cmd.Parameters.Clear();
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if ((Object.Equals(obj, null)) || (Object.Equals(obj, System.DBNull.Value)))
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{
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return null;
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}
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else
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{
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return obj;
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}
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}
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}
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}
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/// <summary>
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/// 执行SQL语句，返回影响的记录数
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/// </summary>
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/// <param name="aSQL">SQL语句</param>
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/// <returns>影响的记录数</returns>
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public int ExecuteSql(string aSQL)
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{
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using (DbConnection conn = _DbFactory.CreateConnection())
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{
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conn.ConnectionString = mDBConfig.ConnString;
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using (DbCommand cmd = _DbFactory.CreateCommand())
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{
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PrepareCommand(cmd, conn, aSQL);
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int rows = cmd.ExecuteNonQuery();
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cmd.Parameters.Clear();
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return rows;
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}
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}
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}
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/// <summary>
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/// 执行SQL语句，返回影响的记录数
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/// </summary>
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/// <param name="aSQLWithParameter">SQL语句及参数</param>
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/// <returns></returns>
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public int ExecuteSql(SQLWithParameter aSQLWithParameter)
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{
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using (DbConnection conn = _DbFactory.CreateConnection())
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{
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conn.ConnectionString = mDBConfig.ConnString;
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using (DbCommand cmd = _DbFactory.CreateCommand())
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{
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PrepareCommand(cmd, conn, aSQLWithParameter.SQL.ToString(), aSQLWithParameter.Parameters);
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int rows = cmd.ExecuteNonQuery();
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cmd.Parameters.Clear();
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return rows;
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}
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}
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}
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/// <summary>
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/// 执行多条SQL语句，实现数据库事务。
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/// </summary>
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/// <param name="aSQLWithParameterList">参数化的SQL语句结构体对象集合</param>
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public string ExecuteSqlTran(List<SQLWithParameter> aSQLWithParameterList)
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{
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using (DbConnection conn = _DbFactory.CreateConnection())
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{
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conn.ConnectionString = mDBConfig.ConnString;
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conn.Open();
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DbTransaction fSqlTransaction = conn.BeginTransaction();
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try
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{
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List<DbCommand> fTranCmdList = new List<DbCommand>();
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//创建新的CMD
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DbCommand fFirstCMD = _DbFactory.CreateCommand();
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fFirstCMD.Connection = conn;
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fFirstCMD.Transaction = fSqlTransaction;
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fTranCmdList.Add(fFirstCMD);
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int NowCmdIndex = 0;//当前执行的CMD索引值
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int ExecuteCount = 0;//已经执行的CMD次数
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StringBuilder fSQL = new StringBuilder();
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foreach (SQLWithParameter fSQLWithParameter in aSQLWithParameterList)
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{
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fSQL.Append(fSQLWithParameter.SQL.ToString() + ";");
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fTranCmdList[NowCmdIndex].Parameters.AddRange(fSQLWithParameter.Parameters.ToArray());
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if (fTranCmdList[NowCmdIndex].Parameters.Count > 2000)
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{ //参数达到2000个，执行一次CMD
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fTranCmdList[NowCmdIndex].CommandText = fSQL.ToString();
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fTranCmdList[NowCmdIndex].ExecuteNonQuery();
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DbCommand fNewCMD = _DbFactory.CreateCommand();
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fNewCMD.Connection = conn;
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fNewCMD.Transaction = fSqlTransaction;
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fTranCmdList.Add(fNewCMD);
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NowCmdIndex++;
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ExecuteCount++;
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fSQL.Clear();//清空SQL
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}
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}
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if (ExecuteCount < fTranCmdList.Count)
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{//已执行CMD次数小于总CMD数，执行最后一条CMD
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fTranCmdList[fTranCmdList.Count - 1].CommandText = fSQL.ToString();
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fTranCmdList[fTranCmdList.Count - 1].ExecuteNonQuery();
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}
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fSqlTransaction.Commit();
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return null;
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}
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catch (Exception ex)
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{
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fSqlTransaction.Rollback();
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StringBuilder fSQL = new StringBuilder();
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foreach (SQLWithParameter fSQLWithParameter in aSQLWithParameterList)
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{
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fSQL.Append(fSQLWithParameter.SQL.ToString() + ";");
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}
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YFmk.Lib.LocalLog.WriteByDate(fSQL.ToString()+" 错误："+ex.Message, "ORM");
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return ex.Message;
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}
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}
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}
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/// <summary>
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/// 执行查询语句，返回DataSet
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/// </summary>
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/// <param name="SQLString">查询语句</param>
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/// <returns>DataSet</returns>
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public DataSet Query(string SQLString)
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{
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using (DbConnection conn = _DbFactory.CreateConnection())
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{
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conn.ConnectionString = mDBConfig.ConnString;
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using (DbCommand cmd = _DbFactory.CreateCommand())
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{
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PrepareCommand(cmd, conn, SQLString);
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using (DbDataAdapter da = _DbFactory.CreateDataAdapter())
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{
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da.SelectCommand = cmd;
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DataSet ds = new DataSet();
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try
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{
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da.Fill(ds, "ds");
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cmd.Parameters.Clear();
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}
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catch (Exception ex)
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{
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}
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return ds;
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}
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}
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}
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}
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/// <summary>
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/// 执行查询语句，返回DataSet
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/// </summary>
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/// <param name="aSQLWithParameter">查询语句</param>
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/// <returns>DataSet</returns>
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public DataSet Query(SQLWithParameter aSQLWithParameter)
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{
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using (DbConnection conn = _DbFactory.CreateConnection())
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{
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conn.ConnectionString = mDBConfig.ConnString;
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using (DbCommand cmd = _DbFactory.CreateCommand())
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{
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PrepareCommand(cmd, conn, aSQLWithParameter.SQL.ToString(), aSQLWithParameter.Parameters);
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using (DbDataAdapter da = _DbFactory.CreateDataAdapter())
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{
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da.SelectCommand = cmd;
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DataSet ds = new DataSet();
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da.Fill(ds, "ds");
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cmd.Parameters.Clear();
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return ds;
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}
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}
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}
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}
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#endregion
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#region 私有函数
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private void PrepareCommand(DbCommand cmd, DbConnection conn, string cmdText)
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{
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if (conn.State != ConnectionState.Open)
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conn.Open();
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cmd.Connection = conn;
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cmd.CommandText = cmdText;
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}
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private void PrepareCommand(DbCommand cmd, DbConnection conn, string cmdText, List<DbParameter> cmdParms)
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{
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if (conn.State != ConnectionState.Open)
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conn.Open();
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cmd.Connection = conn;
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cmd.CommandText = cmdText;
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if (cmdParms != null && cmdParms.Count>0)
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{
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cmd.Parameters.AddRange(cmdParms.ToArray());
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}
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}
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#endregion
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