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