使用ADO.NET访问数据库

using System;
using System.Collections.Generic;
using System.Data.SqlClient;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Demo
{
    class ConnectionDB
    {
        //准备连接字符串
        static string str = "Data Source=.;Initial Catalog=MySchool;User ID=sa;Pwd=1";

        //准备连接对象
        public SqlConnection con = new SqlConnection(str);

        //连接数据库
        public void OpenDB()
        {
            try
            {
                con.Open();
            }
            catch (Exception ex)
            {
                Console.WriteLine("发生异常："+ex);
                
            }
        }

        //关闭数据库
        public void CloseDB()
        {
            con.Close();
        }
    }
}

using System;
using System.Collections.Generic;
using System.Data.SqlClient;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Demo
{
    class User
    {
        ConnectionDB db = new ConnectionDB();
        //登录方法

        public void Login(string loginID, string loginPwd)
        { 
            //步骤一：创建一个Command对象
            string sql = "SELECT COUNT(1) FROM Login WHERE LoginID=‘" + loginID + "‘ AND Loginpwd=‘" + loginPwd + "‘";
            Console.WriteLine(sql);

            //打开数据库连接
            db.OpenDB();
            SqlCommand cmd = new SqlCommand(sql, db.con);
            
            //步骤二：接收数据库返回值
            int count = (int)cmd.ExecuteScalar();

            //步骤三：判断返回值
            if (count>0)
            {
                Console.WriteLine("登录成功");
            }
            else
            {
                Console.WriteLine("登录失败");
            }
      
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data.SqlClient;
namespace Demo
{
    class Program
    {
        static void Main(string[] args)
        {


            #region 连接数据库
            //步骤一：配置参数
            string conn = "Data Source=.;Initial Catalog=MySchool;User ID=sa;Pwd=.";

            //步骤二：创建对象并连接数据库
            SqlConnection co = new SqlConnection(conn);

            //步骤三：打开数据库
            //co.Open();
            //Console.WriteLine("打开数据库连接成功！");

            //步骤N：关闭数据库
            //co.Close();
            //Console.WriteLine("关闭数据库连接成功！");


            #endregion


            #region 处理异常
            try
            {
                co.Open();
                Console.WriteLine("打开数据库连接成功！");
            }
            catch (SqlException ex)
            {
                Console.WriteLine("异常：" + ex);

            }
            finally
            {
                Console.WriteLine("永远都在你身边！");
            }
            #endregion


                #region 登录
                    Console.WriteLine("请输入用户名：");
                    string loginID = Console.ReadLine();
                    Console.WriteLine("请输入密码：");
                    string loginpwd = Console.ReadLine();
                    User user = new User();
                    user.Login(loginID, loginpwd);
                #endregion

                Console.ReadLine();

        }
    }
}