Private SqlConntion con;
Public SqlConntion Con
{
    get
    {
        //连接字符串
        string str="Data Souce=.;Initial Catalog=MySchool;User ID=sa;Pwd=.";
        //如果连接conntion为空的情况下创建
        if(con==null)
        {
        con=new SqlConntion(str);
        }
        return con;
    }
}
//打开数据库连接
public void OpenConntion()
{
    //判断数据库连接是否打开
    if(Con.state==ConntionState.Closed)
    {
        Con.Open();
    }
    //判断数据库连接是否堵塞
    else if(Con.state==ConntionState.Broken)
    {
        Con.Close();
        Con.Open();
    }
}
//关闭数据库连接
public void CloseConntion()
{
    if(Con.state==ConntionState.Open||Con.state==ConntionState.Broken)
    {
        Con.Close();
    }
}