VS2010连接SqlServer2008数据库，Oracle10g数据库，Mysql5.524数据库，Access2013数据库经典教程，不看肯定后悔

  今天看vs2010多态，既然数据库类库都是实现接口的信息，那么我直接使用接口来连接不同数据库，这不是很符合接口的性质哈

  设计了VS2010连接SqlServer2008，Oracle10g，Mysql5.524，Access2013

这是前台窗口

这是后台代码：

using System;
using System.Data;
using System.Configuration;
using System.Windows.Forms;
using System.Data.SqlClient;
using MySql.Data.MySqlClient;
using System.Data.OleDb;
using System.Data.OracleClient;
namespace Main
{
    public partial class Main : Form
    {
        public Main()
        {
            InitializeComponent();
        }

        private void Main_Load(object sender, EventArgs e)
        {
            
        }
        private static string connIStr = null; //存储用户选择的数据库

        private static IDbConnection conn = null;//Connection接口

        private static IDbCommand cmd=null; //Command接口

        private static IDataReader reader;  //读写器接口

        private string queryString = null;//查询命令

        private static string connStr = null; //数据库连接字符串

        private void btnTest_Click(object sender, EventArgs e)
        {
            if (rbAccess.Checked)
            {
                txtQuery.Text = ""; //将TextBox清空，防止数据干扰
                connIStr = "accessConnstr";
                connStr = this.GetConnStr(connIStr);
                conn = new OleDbConnection(connStr);
                queryString = "select * from [User]";
            }
            else if (rbSqlServer.Checked)
            {
                txtQuery.Text = "";
                connIStr = "sqlServerConnstr";
                connStr = this.GetConnStr(connIStr);
                conn = new SqlConnection(connStr);
                queryString = "select * from [User]";
            }
            else if(rbOralce.Checked)
            {
                txtQuery.Text = "";
                connIStr = "oralceConnstr";
                connStr = this.GetConnStr(connIStr);
                conn = new OracleConnection(connStr);
                queryString = "select * from Users";
            }
            
            else if (rbMysql.Checked)
            {
                txtQuery.Text = "";
                connIStr = "mysqlConnstr";
                connStr = this.GetConnStr(connIStr);
                conn = new MySqlConnection(connStr);
                queryString = "select * from User";
                
            }
            this.Connect(conn,cmd,queryString);
        }
        /// <summary>
        /// 进行数据查询
        /// </summary>
        /// <param name="conn"></param>
        /// <param name="cmd"></param>
        /// <param name="reader"></param>
        /// <param name="queryString"></param>
        private void Connect(IDbConnection conn,IDbCommand cmd,string queryString)
        {
            try
            {
                cmd = conn.CreateCommand();
                cmd.CommandText = queryString;//初始化Command对象
                conn.Open(); //打开数据库
                reader = cmd.ExecuteReader();//初始化DataReader对象
                while (reader.Read())
                {
                    //查询单个字段
                    txtQuery.AppendText(reader.GetString(reader.GetOrdinal("UserName"))+"\r\n");
                }
            }
            catch(Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
            finally
            {
                conn.Close();//关闭连接
            }
        }
        /// <summary>
        /// 返回查询字符串
        /// </summary>
        /// <param name="connIStr">查询字符串</param>
        /// <returns></returns>
        private string GetConnStr(string connIStr)
        {
            string connStr = ConfigurationManager.ConnectionStrings[connIStr].ConnectionString;
            return connStr;
        }
    }
    
}

配置文件代码：

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <connectionStrings>
    <!--Access连接vs2010连接字符串-->
    <add name="accessConnstr" connectionString="Provider=Microsoft.ACE.OLEDB.12.0;Data Source=D:\visual studio 2010\Project3\多态，接口\vs连接access\bin\Debug\1.accdb" providerName="Access"/>

    <!--Mysql连接vs2010连接字符串-->
    <add name="mysqlConnstr" connectionString="server=localhost;user id=root;Password=****;database=test;persist security info=False" providerName="Mysql"/>
    
    <!--SqlServer连接vs2010连接字符串-->
    <add name="sqlServerConnstr" connectionString="Data Source=.\SQLEXPRESS;Initial Catalog=Sjms;Integrated Security=True" providerName="SqlServer"/>

    <!--Oracle连接vs2010连接字符串-->
    <add name="oralceConnstr" connectionString="Data Source=Acer-PC;Persist Security Info=True;User ID=****;Password=****" providerName="Oracle"/>
  </connectionStrings>
</configuration>

运行一下，Perfact，查询数据库成功