c#数据库编程

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.SqlClient;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace Experiment
{
    public partial class frmDataBase : Form
    {
        public frmDataBase()
        {
            InitializeComponent();
        }
        //1)创建连接对象
        SqlConnection conn = new SqlConnection();
        //2)创建命令对象
        SqlCommand cmd = new SqlCommand();
        //数据库连接字符串赋值：请根据实际环境生成数据库连接字符串
        string str = @"Data Source=.\SQLEXPRESS;AttachDbFilename=D:\Experiment61\Student.MDF;Integrated Security=True;Connect Timeout=30;User Instance=True";
        private void Form1_Load(object sender, EventArgs e)
        {
            conn.ConnectionString = str;
            conn.Open();
            cmd.Connection = conn;          
        }
        private void menuBrowsing_Click(object sender, EventArgs e)//查看
        {
            //cmd.ExecuteReader获取数据集
            dgvStudentInfo.Visible = true;
            //3)给命令对象CommandText属性赋值
            cmd.CommandText = "select * from student";//选择表的所有字段
            //4)命令执行
            SqlDataReader result = cmd.ExecuteReader();	//获取数据集
            //*将记录集装载到DataTable，以此作为DataGridView的数据源
            DataTable dt = new DataTable();
            dt.Load(result);
            dgvStudentInfo.DataSource = dt;
            dgvStudentInfo.Refresh();
            result.Close();								//关闭数据集
           
        }

        private void menuInsert_Click(object sender, EventArgs e)         //添加
        {
            //根据窗体输入内容，向数据库添加一条数据，
           //暂不考虑主键重复的问题
            cmd.CommandText = @"Insert Into student Values(‘" + txtNo .Text  + "‘,‘" 
                                                                     +txtName .Text  + "‘,‘"
                                                                     + txtSex .Text  + "‘,‘"
                                                                     + txtNative .Text  + "‘,‘"
                                                                     + txtBirth .Text  + "‘,"
                                                                     + txtGrade .Text  + ",‘" 
                                                                     + txtMajor .Text  + "‘)";

            try
            {
                int val = cmd.ExecuteNonQuery();	//执行CommandText所要求的插入记录操作
                if (val > 0)
                    MessageBox.Show("已在表中成功插入指定记录!", "记录插入操作");
                menuBrowsing_Click(sender, e);
                TextBoxClear();
            }
            catch (Exception ex) { MessageBox.Show(ex.ToString(), "记录插入失败！"); }
        }

        private void menuEdit_Click(object sender, EventArgs e)        //修改
        {   
            //根据窗体输入内容，更新数据库中对应学号的数据，即更新条件为学号=选中记录的学号。
          
            cmd.CommandText = @"Update student Set Name=‘" + txtName .Text + "‘,"
                                                        + "Sex=‘" + txtSex .Text  + "‘,"
                                                        + "Native=‘" + txtNative .Text  + "‘,"
                                                        + "Birth=‘" + txtBirth .Text  + "‘,"
                                                        + "Grade=" + txtGrade .Text  + ","
                                                        + "Major=‘" + txtMajor .Text  + "‘" 
                                + "Where No=‘"+txtNo .Text  + "‘" ;
            try
            {
                int val = cmd.ExecuteNonQuery();	   //执行CommandText所要求的修改记录操作
                if (val > 0)
                {
                    MessageBox.Show("表中指定记录修改成功!", "记录修改操作");
                    menuBrowsing_Click(sender, e);
                    TextBoxClear();
                }
                else
                    MessageBox.Show("未在表中找到要修改的记录!", "记录修改失败");
            }
            catch (Exception ex)
            { 
                MessageBox.Show(ex.ToString(), "更新数据失败！"); 
            }
        }

        private void menuDelete_Click(object sender, EventArgs e)//删除
        {
            //将选中数据从数据库删除，即删除条件为学号=选中记录的学号。
            
            cmd.CommandText = "delete from student where No=‘"+txtNo .Text+"‘";
            try
            {
                int val = cmd.ExecuteNonQuery();		//执行CommandText所要求的删除记录操作
                if (val > 0)
                {
                    MessageBox.Show("已在表中成功删除指定记录!", "记录删除操作");
                    menuBrowsing_Click(sender, e);
                    TextBoxClear();
                }
                else
                    MessageBox.Show("表中未找到要删除的记录", "记录删除操作");
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString(), "删除数据失败！"); 
            }
        }

        private void TextBoxClear()
        {
            txtNo.Text = "";
            txtName.Text = "";
            txtSex.Text = "";
            txtNative.Text = "";
            txtBirth.Text = "";
            txtGrade.Text = "";
            txtMajor.Text = "";
        }

        private void dgvStudentInfo_CellClick(object sender, DataGridViewCellEventArgs e)
        {
            int i = e.RowIndex;
      
            txtNo.Text = dgvStudentInfo.Rows[i].Cells[0].Value.ToString();
            txtName.Text = dgvStudentInfo.Rows[i].Cells[1].Value.ToString();
            txtSex.Text = dgvStudentInfo.Rows[i].Cells[2].Value.ToString();
            txtNative.Text = dgvStudentInfo.Rows[i].Cells[3].Value.ToString();
            txtBirth.Text = dgvStudentInfo.Rows[i].Cells[4].Value.ToString();
            txtGrade.Text = dgvStudentInfo.Rows[i].Cells[5].Value.ToString();
            txtMajor.Text = dgvStudentInfo.Rows[i].Cells[6].Value.ToString();
        }
    }
}