C#学习笔记（6）——大项目增删改查

说明（2017-5-28 11:35:39）：

1. 需要注意的地方很多

2. 首先是连接字符串str要直接写在类里面，不然每个按钮里面都要写一遍。

3. 查询用到sqlDataReader等三个方法，其他增删改只用到sqlCommond和sqlConnection。

4. sqlConnection记得要open！

5. 其他的记不起来了，总之要经常练习！

运行结果：

代码：

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;
using System.Data.SqlClient;

namespace _03大项目查找
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();

        }
        string str = "Data Source=.; Initial Catalog=mysql; Integrated Security=True;";

        private void Form1_Load(object sender, EventArgs e)
        {

            loadStudent(0);
        }
        /// <summary>
        /// 加载学生信息
        /// </summary>
        /// <param name="p">p是删除标识，0删除，1未删除</param>
        public void loadStudent(int p)
        {
            List<Student> list = new List<Student>();

            using (SqlConnection con = new SqlConnection(str))
            {
                con.Open();
                string sql = "select id, name, chinese, math, flag from myclass where flag = " + p;
                using (SqlCommand cmd = new SqlCommand(sql, con))
                {
                    using (SqlDataReader reader = cmd.ExecuteReader())
                    {
                        if (reader.HasRows)
                        {
                            while (reader.Read())
                            {
                                Student st = new Student();
                                st.Id = Convert.ToInt32(reader["id"]);
                                st.Name = Convert.ToString(reader["name"]);
                                st.Chinese = Convert.ToString(reader["chinese"]);
                                st.Math = Convert.ToString(reader["math"]);
                                st.Flag = Convert.ToInt32(reader["flag"]);
                                list.Add(st);
                            }
                        }
                    }
                }
            }

            dgv.DataSource = list;
            dgv.SelectedRows[0].Selected = false;
        }
        /// <summary>
        /// 添加学生信息
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void button1_Click(object sender, EventArgs e)
        {
            int n = -999;
            string name = txtName.Text;
            string chinese = txtChinese.Text;
            string math = txtMath.Text;
            string sql = string.Format("insert into myclass(name,chinese,math,flag) values('{0}','{1}','{2}',0)", name, chinese, math);
            using (SqlConnection con = new SqlConnection(str))
            {
                using (SqlCommand cmd = new SqlCommand(sql, con))
                {
                    con.Open();
                    n = cmd.ExecuteNonQuery();
                    MessageBox.Show(n > 0 ? "操作成功！" : "操作失败！");
                }
            }
            loadStudent(0);

            //MessageBox.Show("123");
        }
        /// <summary>
        /// 删除学生
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnDel_Click(object sender, EventArgs e)
        {
            int n = -999;
            string id = dgv.SelectedRows[0].Cells[0].Value.ToString();
            string name = dgv.SelectedRows[0].Cells[1].ToString();
            string chinese = dgv.SelectedRows[0].Cells[2].ToString();

            string sql = string.Format("update myclass set flag = 1 where id ={0}", id);
            using (SqlConnection con = new SqlConnection(str))
            {
                using (SqlCommand cmd = new SqlCommand(sql, con))
                {
                    con.Open();
                    n = cmd.ExecuteNonQuery();
                    MessageBox.Show(n > 0 ? "操作成功！" : "操作失败！s");
                }
            }
            loadStudent(0);
        }
        /// <summary>
        /// 选中一行，显示在修改框中
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void dgv_CellClick(object sender, DataGridViewCellEventArgs e)
        {
            lbId.Text = dgv.SelectedRows[0].Cells[0].Value.ToString();
            txtUname.Text = dgv.SelectedRows[0].Cells[1].Value.ToString();
            txtUchinese.Text = dgv.SelectedRows[0].Cells[2].Value.ToString();
            txtUmath.Text = dgv.SelectedRows[0].Cells[3].Value.ToString();
            
        }

        private void btnUpdate_Click(object sender, EventArgs e)
        {
            int n = -999;
            if (dgv.SelectedRows.Count>0)
            {
                string sql = string.Format("update myclass set name = {0}, chinese = {1}, math = {2} where id = {3}", txtUname.Text,txtUchinese.Text,txtUmath.Text,lbId.Text);
                using (SqlConnection con = new SqlConnection(str))
                {
                    using (SqlCommand cmd = new SqlCommand(sql,con))
                    {
                        con.Open();
                        n = cmd.ExecuteNonQuery();
                        MessageBox.Show(n>0?"操作成功！":"操作失败！");
                    }
                }
            }
            else
            {
                MessageBox.Show("请输入数据！");
            }
            loadStudent(0);
        }
    }
}