三层架构补充

第一、DAL、BLL、Model必须为类库，UI可以为控制台、winform、asp.net等；

第二、SqlHelper放在DAL中，但ConnectionString配置在UI的config中，这是因为ConfigurationManager是读取UI项目（入口启动项目）的config；

第三、Executescalar(),ExecuteReader()不仅可以用来执行select查询，还可以用来执行insert等操作；

第四、ADO.Net中想给SqlParameter的参数赋值null的话，必须传递Dbnull.Value;

第五、在c#代码中写sql语句bool类型数据必须写1或0；

案例：

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

namespace SanCeng.DAL
{
    public class UserDAL
    {
        /// <summary>
        /// 新增
        /// </summary>
        /// <param name="userName"></param>
        /// <param name="password"></param>
        /// <param name="phoneNum"></param>
        /// <param name="age"></param>
        /// <returns></returns>
        public long Add(string userName, string password, string phoneNum, int? age)
        {
           object obj = SqlHelper.ExecuteScalar("insert into T_Users(UserName,Password,PhoneNum,Age,IsDeleted) output inserted.id values(@UserName,@Password,@PhoneNum,@Age,0)", new SqlParameter("@UserName", userName), new SqlParameter("@Password", password), new SqlParameter("@PhoneNum", phoneNum),new SqlParameter("@Age",age==null?(object)DBNull.Value:age));
            return Convert.ToInt64(obj);
        }

        /// <summary>
        /// 软删除id为主键的数据
        /// </summary>
        /// <param name="id"></param>
        public void Delete(long id)
        {
            SqlHelper.ExecuteNonQuery("Update T_Users set IsDeleted=1 where id=@Id", new SqlParameter("@Id", id));
        }
        private User ToUser(DataRow row)
        {
            User user = new User();
            user.Id = (long)row["Id"];
            user.Age = row.IsNull("Age") ? null : (int?)row["Age"];
            user.Password = (string)row["Password"];
            user.IsDeleted = (bool)row["IsDeleted"];
            user.phoneNum = (string)row["UserName"];
            user.UserName = (string)row["UserName"];
            return user;
        }

        public void Update(User user)
        {
            SqlHelper.ExecuteNonQuery("Update T_Users set UserName=@UserName,Password=@Password,PhoneNum=@PhoneNum,Age=@Age where Id=@Id", new SqlParameter("@UserName", user.UserName), new SqlParameter("@Password", user.Password), new SqlParameter("@PhoneNum", user.phoneNum), new SqlParameter("@Age", user.Age == null ? (object)DBNull.Value : user.Age), new SqlParameter("@Id", user.Id));
        }
        public User GetById(long id)
        {
           DataTable table = SqlHelper.ExecuteQuery("select * from T_Users where Id=@Id", new SqlParameter("@Id", id));
            if(table.Rows.Count<=0)
            {
                return null;
            }
            else if(table.Rows.Count>1)
            {
                throw new ApplicationException("找到多条id="+id+"的数据");
            }
            else
            {
                DataRow row = table.Rows[0];
                return ToUser(row);
            }
        }
        /// <summary>
        /// 返回所有未软删除的数据
        /// </summary>
        /// <returns></returns>
        public IEnumerable<User> GetAll()
        {
            DataTable dt = SqlHelper.ExecuteQuery("select * fom T_User where IsDeleted = 0");
            List<User> list = new List<User>();
            foreach(DataRow row in dt.Rows)
            {
                list.Add(ToUser(row));
            }
            return list;
        }
    }



}

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

namespace SanCeng.DAL
{
    class SqlHelper
    {
        private static string connStr = ConfigurationManager.ConnectionStrings["connstr"].ConnectionString;
        public static  void ExecuteNonQuery(string sql, params SqlParameter[] parameters)
        {
            using (SqlConnection conn = new SqlConnection(connStr))
            using (SqlCommand cmd = conn.CreateCommand())
            {
                conn.Open();
                cmd.CommandText = sql;
                cmd.Parameters.AddRange(parameters);
                cmd.ExecuteNonQuery();
            }
        }
        public static  object ExecuteScalar(string sql, params SqlParameter[] parameters)
        {
            using (SqlConnection conn = new SqlConnection(connStr))
            using (SqlCommand cmd = conn.CreateCommand())
            {
                conn.Open();
                cmd.CommandText = sql;
                cmd.Parameters.AddRange(parameters);
                return cmd.ExecuteScalar();
            }
        }
        public static DataTable ExecuteQuery(string sql, params SqlParameter[] parameters)
        {
            DataTable table = new DataTable();
            using (SqlConnection conn = new SqlConnection(connStr))
            using (SqlCommand cmd = conn.CreateCommand())
            {
                conn.Open();
                cmd.CommandText = sql;
                cmd.Parameters.AddRange(parameters);
                using (SqlDataReader reader = cmd.ExecuteReader())
                {
                    table.Load(reader);
                    return table;
                }
            }
        }
    }
}

using SanCeng.DAL;
using SanCeng.Model;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace SanCeng.BLL
{
    public class UserBLL
    {
        private UserDAL uDAL = new UserDAL();
        public long Add(string userName,string password,string phoneNum,int? age)
        {
            return uDAL.Add(userName, password, phoneNum, age);
        }
        public void Delete(long id)
        {
            uDAL.Delete(id);
        }
        public void Update(User user)
        {
            uDAL.Update(user);
        }
        public User GetById(long id)
        {
            return uDAL.GetById(id);
        }
        public IEnumerable<User> GetAll()
        {
            return uDAL.GetAll();
        }
    }
}

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

namespace SanCeng.Model
{
    public class User
    {
        public long Id { get; set; }
        public int? Age { get; set; }
        public string phoneNum { get; set; }
        public string Password { get; set; }
        public bool IsDeleted { get; set; }
        public string UserName { get; set; }
    }
}

using SanCeng.BLL;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace SanCeng.WinForm
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            UserBLL bll = new UserBLL();
            
            bll.Delete(1);
        }
    }
}