实体类的高级应用

最新推荐文章于 2024-11-05 16:57:37 发布

柠檬不萌耶

最新推荐文章于 2024-11-05 16:57:37 发布

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本文链接：https://blog.youkuaiyun.com/qq_36074150/article/details/65450832

本文介绍了一个使用C#开发的课程选择系统，该系统能够根据用户选择的年级动态加载对应的科目列表。通过连接到数据库并执行参数化的SQL查询，确保了数据的安全性和准确性。

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.Threading.Tasks;
using System.Windows.Forms;

namespace Day05_0100
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void cboGrade_SelectedIndexChanged(object sender, EventArgs e)
        {
            #region 内存操作
            //write what 写什么
            //1.User select which grade 
            //string gradeName = cboGrade.Text;
            //if (gradeName.Equals("S1"))
            //{
            //    cboSubject.Items.Clear();
            //    cboSubject.Items.Add("S1----Java");
            //    cboSubject.Items.Add("S1----SQL");
            //    cboSubject.Items.Add("S1----C#");

            //}
            //else if (gradeName.Equals("S2"))
            //{
            //    cboSubject.Items.Clear();
            //    cboSubject.Items.Add("S2----Java");
            //    cboSubject.Items.Add("S2----SQL");

            //} 
            #endregion

           
            

            string gradename = cboGrade.Text;
            int gradeid= GetIdByName(gradename);
            string str = "Data Source=.;Initial Catalog=MySchool;Integrated Security=True";
            SqlConnection con = new SqlConnection(str);
            string sql = "select * from subject where gradeid=@gid";
            SqlParameter para=new SqlParameter("@gid",gradeid);
            SqlCommand cmd = new SqlCommand(sql, con);
            cmd.Parameters.Add(para);
            SqlDataAdapter da=new SqlDataAdapter();
            da.SelectCommand = cmd;
            DataSet ds=new DataSet();
            da.Fill(ds,"subjectInfo");
            cboSubject.DataSource = ds.Tables["subjectInfo"];
            cboSubject.ValueMember = "subjectid";
            cboSubject.DisplayMember = "subjectname";

            if (ds.Tables["subjectInfo"].Rows.Count == 0)
            {
                ds.Tables["subjectInfo"].Clear();
            }


        }

        private int GetIdByName(string gradename)
        {
            string str = "Data Source=.;Initial Catalog=MySchool;Integrated Security=True";
            SqlConnection con = new SqlConnection(str);
            string sql = "select gradeid from grade where gradename='"+gradename+"'";
            SqlCommand cmd=new SqlCommand(sql,con);
            con.Open();

            int gradeid=Convert.ToInt32(cmd.ExecuteScalar());
            con .Close();
            return gradeid;
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            string str = "Data Source=.;Initial Catalog=MySchool;Integrated Security=True";
            SqlConnection con = new SqlConnection(str);
            string sql = "select * from grade";
            SqlDataAdapter da=new SqlDataAdapter(sql,con);
            DataSet ds=new DataSet();
            da.Fill(ds, "gradeInfo");
            cboGrade.DataSource = ds.Tables[0];
            cboGrade.DisplayMember = "gradeName";
            cboGrade.ValueMember = "gradeid";
        }
    }
}