在SQL Server数据库编写通用数据访问方法

using System;
using System.Data;
using System.Data.Common;
using System.Data.SqlClient;
using System.Data.OleDb;
using System.Data.OracleClient;


namespace DAL
{
   public enum DatabaseType
   {
Access,
SQLServer,
Oracle
// 任何其他数据源类型
   }

   public enum ParameterType
   {
Integer,
Char,
VarChar
// 定义公用参数类型集
   }

   public class DataFactory
   {
private DataFactory(){}

public static IDbConnection CreateConnection
   (string ConnectionString, 
   DatabaseType dbtype)
{
   IDbConnection cnn;

   switch(dbtype)
   {
case DatabaseType.Access:
   cnn = new OleDbConnection
(ConnectionString); 
   break;
case DatabaseType.SQLServer:
   cnn = new SqlConnection
(ConnectionString); 
   break;
case DatabaseType.Oracle:
   cnn = new OracleConnection
(ConnectionString);
   break;
default:
   cnn = new SqlConnection
(ConnectionString); 
   break;   
   }

   return cnn;
}


public static IDbCommand CreateCommand
   (string CommandText, DatabaseType dbtype,
   IDbConnection cnn)
{
   IDbCommand cmd;
   switch(dbtype)
   {
case DatabaseType.Access:
   cmd = new OleDbCommand
(CommandText,
(OleDbConnection)cnn);
   break;

case DatabaseType.SQLServer:
   cmd = new SqlCommand
(CommandText,
(SqlConnection)cnn); 
   break;

case DatabaseType.Oracle:
   cmd = new OracleCommand
(CommandText,
(OracleConnection)cnn);
   break;
default:
   cmd = new SqlCommand
(CommandText,
(SqlConnection)cnn); 
   break;
   }

   return cmd;
}


public static DbDataAdapter CreateAdapter
   (IDbCommand cmd, DatabaseType dbtype)
{
   DbDataAdapter da;
   switch(dbtype)
   {
case DatabaseType.Access:
   da = new OleDbDataAdapter
((OleDbCommand)cmd); 
   break;

case DatabaseType.SQLServer:
   da = new SqlDataAdapter
((SqlCommand)cmd); 
   break;

case DatabaseType.Oracle:
   da = new OracleDataAdapter
((OracleCommand)cmd); 
   break;

default:
   da = new SqlDataAdapter
((SqlCommand)cmd); 
   break;
   }

   return da;
}
   }
}