C# datagrideview插件的使用

 private void btnLogin_Click(object sender, EventArgs e)
        {
            string txtUserName = this.txtUserName.Text.Trim();
            string txtPwd = this.txtPwd.Text.Trim();
            if (txtUserName==null||txtPwd==null||txtUserName.Length==0||txtPwd.Length==0)
            {
                MessageBox.Show("您输入的内容为空，请重新输入！");
            }
            string connString = "server=.;database=StudentMISDB;uid=sa;pwd=123456";
            SqlConnection conn = new SqlConnection(connString);
            conn.Open();
            string sql = @"select l.*,DATEDIFF(MI,LoginErrorLastTime,GETDATE()) as 间隔 from login as l where loginname='{0}'";
            sql = string.Format(sql, txtUserName);
            SqlCommand cmd = new SqlCommand(sql,conn);
            SqlDataAdapter adapter = new SqlDataAdapter(cmd);
            DataSet dSet = new DataSet();
            adapter.Fill(dSet);
            conn.Close();
            if (dSet.Tables[0].Rows.Count > 0)
            {
                int errorCount = Convert.ToInt32(dSet.Tables[0].Rows[0][3]);
                int times = Convert.ToInt32(dSet.Tables[0].Rows[0][5]);
                if (errorCount >= 3 && times <= 15)
                {
                    if (dSet.Tables[0].Rows[0][1].ToString() == txtUserName && dSet.Tables[0].Rows[0][2].ToString()==txtPwd)
                    {
                        MessageBox.Show("登陆成功");
                        conn.Open();
                        string uptateSql = @"update login set loginerrorcount=0 where id='{0}'";
                        uptateSql = string.Format(uptateSql,dSet.Tables[0].Rows[0][0].ToString());
                        cmd = new SqlCommand(uptateSql,conn);
                        cmd.ExecuteNonQuery();
                        conn.Close();
                    }
                    else
                    {
                        MessageBox.Show("登录名或者密码错误！");
                        conn.Open();
                        string updateSql = @"update login set loginerrorcount=loginerrorcount+1 ,loginerrorlasttime=getdate() where id='{0}'";
                        updateSql = string.Format(updateSql,dSet.Tables[0].Rows[0][0].ToString());
                        cmd = new SqlCommand(updateSql,conn);
                        cmd.ExecuteNonQuery();
                        conn.Close();
                    }
                }
                else
                {
                    MessageBox.Show("请在"+(15-times)+"分钟后登录！");
                }
            }
            else
            {
                MessageBox.Show("用户不存在！");
            }
        }
    }

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 ADO.NET8._30
{
    public partial class DataGridView : Form
    {
        public DataGridView()
        {
            InitializeComponent();
        }

        private void DataGridView_Load(object sender, EventArgs e)
        {
            //加载学生选课信息
            loadStudntData();
            //加载课程信息（没有选的课程）
            LoadCourse();
        }
        /// <summary>
        /// 自定义一个方法
        /// </summary>
        private void LoadCourse()
        {
            //1.创建数据库连接符
            string connString = "server=.;database=StudentMISDB;uid=sa;pwd=123456";
            //2.链接数据库
            SqlConnection conn = new SqlConnection(connString);
            //3.添加数据库要执行的语句，通过ID查找没有选择到的课程
            string sql = @"select * from Course where CourseId not in(select distinct sc.CourseId from  [dbo].[Students] as s
                join  Score as sc on s.StudentId=sc.StudentId
                join  Course as c on sc.CourseId = c.CourseId
                where s.StudentId='2')";
            //4.创建命令
            SqlCommand cmd = new SqlCommand(sql, conn);
            //5.断开式连接查询
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            //6.创建数据缓冲区（数据集）
            DataSet ds = new DataSet();
            conn.Open();
            //7.填充数据集
            da.Fill(ds);
            conn.Close();
            //8.绑定数据源
            this.cmbCourseName.DataSource = ds.Tables[0];
            
            //9.设置combobox控件中要显示的列
            //this.cmboxCourse.DisplayMember = "列名";
            this.cmbCourseName.DisplayMember = "Name";
            //10.DisplayMember绑定需要显示的数据表字段，而ValueMember绑定需要获取选择的项的值；直接可见的是此item的 DisplayMember 对应内容，而此 item的值是ValueMember 的对应内容。
            this.cmbCourseName.ValueMember = "CourseId";
        }
        /// <summary>
        /// 获取选中的值
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void cmbCourseName_SelectedIndexChanged(object sender, EventArgs e)
        {
            string courseID = this.cmbCourseName.SelectedValue.ToString();
            ///string courseName = this.cmboxCourse.SelectedText;
        }
        /// <summary>
        /// 保存 选课后，
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnSave_Click(object sender, EventArgs e)
        {
            //获取到在combobox控件中已经选择的值
            string courseID = this.cmbCourseName.SelectedValue.ToString();
            //string courseName = this.cmboxCourse.SelectedText;
            int studentId = 2;
            //1.
            string connString = "server=.;database=StudentMISDB;uid=sa;pwd=123456";
            SqlConnection conn = new SqlConnection(connString);

            string sql = "insert into Score values('{0}','{1}','{2}')";
            sql = string.Format(sql, studentId, courseID, 0);

            SqlCommand cmd = new SqlCommand(sql, conn);
            conn.Open();
            int result = cmd.ExecuteNonQuery();
            conn.Close();
            if (result > 0)
            {
                MessageBox.Show("保存成功");

                loadStudntData();
                LoadCourse();
            }
            else
            {
                MessageBox.Show("保存失败");
            }
        }
        /// <summary>
        /// 加载学生选课信息
        /// </summary>
        private void loadStudntData()
        {
            string connString = "server=.;database=StudentMISDB;uid=sa;pwd=123456";
            SqlConnection conn = new SqlConnection(connString);

            string sql = @"select s.Studentid,c.courseId, s.Name as 姓名,c.Name as 课程名, sc.Score as 成绩 from  [dbo].[Students] as s
                join  Score as sc on s.StudentId=sc.StudentId
                join  Course as c on sc.CourseId = c.CourseId
                where s.StudentId='{0}'";
            sql = string.Format(sql, 2);

            SqlCommand cmd = new SqlCommand(sql, conn);
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            DataSet ds = new DataSet();
            conn.Open();
            da.Fill(ds);
            conn.Close();

            this.dataGridView1.DataSource = ds;
            this.dataGridView1.DataMember = ds.Tables[0].TableName;
        }
    }
}

 二、（1）封装的类：

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

namespace Demo2
{
public static    class SqlCommon
    {

        /// <summary>
        /// 连接字符串
        /// </summary>
        public static string connString = "server=.;database=StudentMISDB;uid=sa;pwd=123456";

        /// <summary>
        /// 执行增删改操作
        /// </summary>
        /// <param name="sql">sql语句 参数传入</param>
        /// <returns></returns>
        public static int ExecuteSql(string sql)
        {
            int result = 0;
            //创建连接对象new SqlConnection( 连接字符串)
            SqlConnection conn = new SqlConnection(connString);
            //创建命令对象  new SqlCommand(sql语句, conn)
            SqlCommand cmd = new SqlCommand(sql, conn);
            // 打开数据连接
            conn.Open();
            // 执行 sql 命令，返回受影响的行数
            result = cmd.ExecuteNonQuery();
            // 关闭数据连接
            conn.Close();
            // 把执行结果【受影响的行数】，返回给调用者
            return result;
        }


        public static DataSet ExecuteQuery(string sql) {

            SqlConnection conn = new SqlConnection(connString);
            SqlCommand cmd = new SqlCommand(sql, conn);
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            DataSet ds = new DataSet();
            conn.Open();
            da.Fill(ds);
            conn.Close();

            return ds;
        }
    }
}

 （二）、调用类

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 Demo2
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void btnAdd_Click(object sender, EventArgs e)
        {
            /// 定义变量接收  用户输入的值
            string loginName = this.txtLoginName.Text.Trim();
            string pwd = this.txtPWD.Text.Trim();

            ///判断用户是否有输入值
            if (loginName == "" || loginName == null)
            {
                MessageBox.Show("请输入用户名");
                return;
            }
            //string.IsNullOrEmpty(字符串) ==>判断字符串是否为“空字符”或为 null
            if (string.IsNullOrEmpty(pwd))
            {
                MessageBox.Show("请输入密码");
                return;
            }


            if (isExistsLoginName(loginName))
            {
                MessageBox.Show("该用户名已经存在，请重新输入");
                this.txtLoginName.Text = string.Empty;
                this.txtPWD.Text = string.Empty;
                return;
            }

            string sql = @"insert  into LoginInfo (loginName,pwd,LoginErrorLastTime)  
            values('{0}','{1}','{2}')";
            sql = string.Format(sql, loginName, pwd, DateTime.Now.ToString());

            int row = SqlCommon.ExecuteSql(sql);
            if (row > 0)
            {
                MessageBox.Show("添加成功");
            }
            else
            {
                MessageBox.Show("添加失败");
            }

        }


        #region 判断 用户名是否存在

        private bool isExistsLoginName(string loginName)
        { 
            string sql = @"select * from LoginInfo where LoginName='{0}'";
            sql = string.Format(sql, loginName);
            DataSet ds = SqlCommon.ExecuteQuery(sql);
            return ds.Tables[0].Rows.Count > 0;
        }
        #endregion
    }
}

 （三）、datagrideview插件

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 Demo2
{
    public partial class FrmScore : Form
    {
        public FrmScore()
        {
            InitializeComponent();
        }

        private void btnSelect_Click(object sender, EventArgs e)
        {
            string name = this.txtCourse.Text.Trim();

            string sql = @"select ScoreId,Name,Score from Course as c
            join Score as sc on c.CourseId = sc.CourseId
            where sc.StudentId='1' and c.Name like '%{0}%'";
            sql = string.Format(sql,name);
            DataSet ds = SqlCommon.ExecuteQuery(sql);

            this.dataGridView1.DataSource = ds.Tables[0];

        }
    }
}