使用DataReader读取数据即查询所有学生

一：这次主要整理上次课在学生信息管理中添加一个学生列表，并显示处理

即在

显示如下：

二：具体操作如下：

首先在数据访问层添加查询所有学生的功能：

代码如下：

 //查询所有学生
        public List<Student> getAll() {

            List<Student> list = new List<Student>();
            string s = "server=.;database=SampleDb;Integrated Security=true;";
            SqlConnection conn = new SqlConnection(s);
            SqlCommand cmd = new SqlCommand();
            cmd.CommandText = "select * from  student";
            cmd.Connection = conn;
            conn.Open();
            SqlDataReader reader = cmd.ExecuteReader();
            while (reader.Read()) {
                Student student = new Student();
                student.Id = (string)reader["id"];
                student.Name = (string)reader["name"];
                student.Gender = (string)reader["gender"];
                student.Major = (string)reader["major"];
                student.Grade = (int)reader["grade"];
                student.TheClass = (int)reader["class"];
                list.Add(student);
            }
            reader.Close();
            conn.Close();
            return list;
        }

为啦便于代码的复用，特抽出一个DbHelper类，实现与数据库的连接：

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

namespace MySchoolDAL
{
   public class DbHelper
   {
       public static void myExecute(string sql)
       {
           string s = "server=.;database=SampleDb;Integrated Security=true;";
           SqlConnection conn = new SqlConnection(s);
           SqlCommand cmd = new SqlCommand();
           cmd.CommandText = sql;
           cmd.Connection = conn;
           conn.Open();
           cmd.ExecuteNonQuery();
           conn.Close(); 
       }

    }
}

然后在业务逻辑层调用数据访问层的显示所有学生的功能：

  public List<Student> getALl() {
            StudentDal dal = new StudentDal();
            return dal.getAll();
        
        }

最后在用户界面层学生列表窗口下，双击button1,实现调用业务逻辑层：

 private void 查看_Click(object sender, EventArgs e)
        {
            StudentBll bll = new StudentBll();
            List<Student> list = bll.getALl();
            gride.DataSource = list;
        }

还忘啦一点就是，调用get  set方法，在实体类中封装字段

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

namespace MySchoolEntity
{
    public  class Student
    {
        public string Id { get; set; }
        public string Name { get; set; }
        public string Gender { get; set; }
        public string Major { get; set; }
        public int Grade { get; set; }
        public int TheClass { get; set; }
    }
}

为了提高代码的复用，顾将studentDal.cs与数据库连接的代码放到DbHelper.cs中

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.SqlClient;
using MySchoolEntity;
namespace MySchoolDAL
{
    public class StudentDal
    {
        public void insert(Student student) { string sql = string.Format("insert into Student(Id,Name,Gender,Major,Grade,Class) values('{0}','{1}','{2}','{3}',{4},{5})", student.Id, student.Name,student.Major, student.Gender, student.Grade, student.TheClass); DbHelper.myExecute(sql);
        }
        public void delete(string id)
        {
            string sql = string.Format("delete from student where id='{0}'", id);
            DbHelper.myExecute(sql);
        
        }
        //查询所有学生
        public List<Student> getAll() {

            List<Student> list = new List<Student>();
            SqlConnection conn = DbHelper.createConnection();
            SqlCommand cmd = new SqlCommand();
            cmd.CommandText = "select * from  student";
            cmd.Connection = conn;
            conn.Open();
            SqlDataReader reader = cmd.ExecuteReader();
            while (reader.Read()) {
                Student student = new Student();
                student.Id = (string)reader["id"];
                student.Name = (string)reader["name"];
                student.Gender = (string)reader["gender"];
                student.Major = (string)reader["major"];
                student.Grade = (int)reader["grade"];
                student.TheClass = (int)reader["class"];
                list.Add(student);
            }
            reader.Close();
            conn.Close();
            return list;
        }

    }
}

DbHelper.cs如下：

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

namespace MySchoolDAL
{
   public class DbHelper
   {
    
       public static void myExecute(string sql)
       {
          
           SqlConnection conn = new SqlConnection();
           conn.ConnectionString = connStr;
           SqlCommand cmd = new SqlCommand();
           cmd.CommandText = sql;
           cmd.Connection = conn;
           conn.Open();
           cmd.ExecuteNonQuery();
           conn.Close(); 
       }

       public static SqlConnection createConnection()
       { string connStr = "server=.;database=SampleDb;Integrated Security=true;";
           return new SqlConnection(connStr); 
       
       }
    }
}