前言

在偷懒和学习之间还是选择敲一遍。这种感觉很踏实。下面是关于三层登陆我的收获。

三层登陆

显示层（UI），业务逻辑层（BLL），数据访问层（DAL）
三层登陆需要引用，U层引用B层，B层引用D层。里面的User需要贯穿三层，为了较少耦合度，所以将User单独拿出来，用三层去引用这个独立层就好了。

代码展示

U层

//这里要增加一个命名空间
using System.Data;
using System.Data.SqlClient;

namespace LoginUI //-------------U层
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            //IDbConnection conn = new SqlConnection("c...");
            //IDbCommand cmd = conn.CreateCommand();
            //cmd.CommandText = "Select UserName From Users where...";
            //cmd.ExecuteReader();

            string userName = txtUserName.Text.Trim();//将文本中的姓名赋值给新的变量userName
            string passWord = txtPassword.Text;
            Login.BLL.LoginManager mgr = new Login.BLL.LoginManager();//实例化Login.BLL.LoginManager
            Login .Model .UserInfo user = mgr.UserLogin(userName, passWord);//把U层的传入实体

            MessageBox.Show("登陆用户："+user.UserName );
        }
    }
}

B层

namespace Login.BLL//------------B层
{
    public class LoginManager
    {
        public Login .Model .UserInfo UserLogin(string userName, string passWord)
        {
            //throw new NotImplementedException();
            Login.DAL.UserDAO uDao = new Login.DAL.UserDAO();//需要引用D层
            Login .Model.UserInfo user= uDao.SelectUser(userName, passWord);

            if (user != null)
            {
                Login.DAL.ScoreDAO sDao = new Login.DAL.ScoreDAO();
                sDao.UpdateScore(userName, 10);
                return user;   //---------将实体user返回U层就好
            }
            else
            {
                throw new Exception("登陆失败");
            }
        }
    }
}

D层

namespace Login.DAL//-----------D层
{
    public class UserDAO//----用户
    {
        public Login.Model .UserInfo SelectUser(string userName,string passWord)
        {
            using (SqlConnection conn = new SqlConnection(DbUtil.ConnString))
            {
                SqlCommand cmd = conn.CreateCommand();
                cmd.CommandText = @"SELECT ID,UserName,Password,Email FROM USERS WHERE UserName = @UserName AND Password=@Password";
                cmd.CommandType = CommandType.Text;

                cmd.Parameters.Add(new SqlParameter("@UserName", userName));
                cmd.Parameters.Add(new SqlParameter("@Password", passWord));

                conn.Open(); //打开数据库

                SqlDataReader reader = cmd.ExecuteReader();

                Login.Model.UserInfo user = null;
                while (reader.Read())
                {
                    if (user == null)
                    {
                        user = new Login.Model.UserInfo();
                    }
                    user.ID = reader.GetInt32(0);
                    user.UserName = reader.GetString(1);
                    user.Password = reader.GetString(2);
                    if (!reader.IsDBNull(3))
                    {
                        user.Email = reader.GetString(3);
                    }

                   // return user;注意返回值在括号外面
                }
                return user;
            }
        }
    }
}

namespace Login.DAL
{
    public class ScoreDAO    //积分类
    {
        public void UpdateScore(string userName, int value)//积分
        {
            using (SqlConnection conn = new SqlConnection(DbUtil.ConnString))
            {
                SqlCommand cmd = conn.CreateCommand();
                cmd.CommandText = @"INSERT INTO SCORES(UserName,Score) Values(@UserName,@Score)";
                cmd.Parameters.Add(new SqlParameter("@UserName", userName));
                cmd.Parameters .Add (new SqlParameter ("@Score",value));

                conn.Open();  //打开数据库
                cmd.ExecuteNonQuery();
            }
        }
    }
}

public class DbUtil       //单独数据库类
    {
        public static string ConnString = @"server = LOVQ-G\SQLEXPRESS;database = Login; User ID = sa;Password=123";  
        //数据库名称+服务器+用户名密码
    }

实体层

namespace Login.Model//独立层
{
    public class UserInfo
    {
        public int ID { get; set; }
        public string UserName { get; set; }
        public string Password { get; set; }
        public string Email { get; set; }

    }
}