ADOnet

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
using System.Data.Common;
using System.Configuration;
using System.Data.sqlClient;
using System.Data.OleDb;
using System.Data.Odbc;

namespace readxml.DB
{
    public class DbHelper: IDbAction
    {
        private DbHelper() 
        { 

        }
        enum DataProvider 
        {
            sqlServer,OleDb,Odbc
        }
        private static DbHelper dbhelper;
        private static object _lock = new object();
        string connString = ConfigurationManager.AppSettings["DB_CONN_STR"]; 
        public static DbHelper DBHelper 
        {
            get 
            {
                lock (_lock) 
                {
                    if (dbhelper == null)
                    {
                        dbhelper = new DbHelper();
                    }

                    return dbhelper;
                }
            }
        }
        /// <summary>
        /// 获取数据库连接
        /// </summary>
        /// <param name="dp"></param>
        /// <returns></returns>
        private IDbConnection GetConnection(DataProvider dp) 
        {
            switch (dp)
            {
                case DataProvider.sqlServer:
                    {
                        return new sqlConnection(connString);
                    }
                case DataProvider.Odbc: 
                    {
                        return new OdbcConnection(connString);
                    }
                case DataProvider.OleDb: 
                    {
                        return new OleDbConnection(connString);
                    }
                default:
                    throw new Exception("xxxxxxxxxxxx");
            }
        }
        /// <summary>
        /// 打开数据库连接
        /// </summary>
        /// <param name="conn"></param>
        private void OpenConnection(IDbConnection conn) 
        {
            conn.open();
        }
        /// <summary>
        /// 数据查询
        /// </summary>
        /// <param name="sql"></param>
        /// <returns></returns>
        public DataTable ExecuteQuery(string sql)
        {
            DataSet ds = new DataSet();
            try
            {
                sqlConnection conn = GetConnection(DataProvider.sqlServer) as sqlConnection;
                OpenConnection(conn);
                sqlCommand command = new sqlCommand(sql,conn);
                sqlDataAdapter adapter = new sqlDataAdapter(command);
                adapter.Fill(ds);
                conn.Close();
            }
            catch (Exception e)
            {
                throw e;
            }            
            return ds.Tables[0];
        }
    }
}