实体类的高级应用

来源：互联网发布：水质监测数据分析编辑：程序博客网时间：2024/06/08 14:10
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";        }    }}
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