實驗反饋5

本週完成了對管理員操作的Student表、Course表、SC表的增刪改查操作，這些操作比上週更加完善了。

現在對Student表的操作沒有問題了。Course表和SC表還有一些問題需要解決。

1、增加或刪除時可以增刪多個成員信息，之前只能操作一個，必須重新啓動纔可以。

解決方法：將this.Dispose()改爲this.Close()。

 

Close後數據庫連接可以再次打開，被關閉的對象還可以再次使用；而Dispose後連接字符串被清空，連接不能再打開。

對C#中Dispose和Close的淺析

2、修改時對於Course表可以通過Cno一次修改一條記錄，增加了通過課程名一次修改多門相同類型的課程的信息。

3、查找時，不僅可以根據主碼查找，還增加了模糊查詢，可以通過任意一種方式查詢。

 

對Course和SC表還存在一些問題需要改進，在增加時輸入的信息不能爲空，否則會出現輸入的數據有誤；SC表的查詢不能只通過Sno和Cno查詢。

Couse表的代碼：

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 dazuoye2
{
    public partial class Admin_Course : Form
    {
        public Admin_Course()
        {
            InitializeComponent();
        }

        private void Admin_Course_Load(object sender, EventArgs e)
        {
            // TODO: 這行代碼將數據加載到表“schoolDataSet1.Course”中。您可以根據需要移動或刪除它。
            this.courseTableAdapter.Fill(this.schoolDataSet1.Course);

        }

        public void clear()
        {
            textBoxcno.Text = "";
            textBoxcname.Text = "";
            textBoxcpno.Text = "";
            textBoxcredit.Text = "";
        }
        SqlConnection con = new SqlConnection("Data Source =.; Initial Catalog = School;  Persist Security Info = True;User ID = sa; Password = 123"); //連接數據庫

        //public string CouCcredit { get; private set; }

        public string EMPTY_Cno(string obj)//輸入的數據Cpno爲空時的情況
        {
            if (obj == null)
                return DBNull.Value.ToString();
            return obj;
        }
        private void buttonadd_Click(object sender, EventArgs e)//增加
        {
            string CouCno = textBoxcno.Text.Trim();
            string CouCname = textBoxcname.Text.Trim();
            string CouCpno =EMPTY_Cno(textBoxcpno.Text);
            string CouCcredit = textBoxcredit.Text.Trim();
            try
            {

                con.Open();     //打開數據庫
                string insertCou = "INSERT INTO Course(Cno,Cname,Cpno,Ccredit)" + "VALUES('" + CouCno + "','" + CouCname + "','" + CouCpno + "'," + CouCcredit+ ")";
                SqlCommand cmd = new SqlCommand(insertCou, con);
                cmd.ExecuteNonQuery();      //將增加後的信息直接出來
            }
            catch
            {
                MessageBox.Show("輸入數據違反要求！");
            }
            finally 
            {
                con.Close();
            }
            this.courseTableAdapter.Fill(this.schoolDataSet1.Course);
        }

        private void buttonclose_Click(object sender, EventArgs e)
        {
            this.Close();
        }

        private void buttondelete_Click(object sender, EventArgs e)//刪除
        {
            try
            {
                con.Open();     //打開數據庫
                string select_Cno = dataGridView1.SelectedRows[0].Cells[0].Value.ToString();//選擇的當前行第一列的值，也就是Cno
                string delete_by_Cno = "DELETE FROM Course WHERE Cno='" + select_Cno + "'";//sql刪除語句
                SqlCommand cmd = new SqlCommand(delete_by_Cno, con);
                cmd.ExecuteNonQuery();
            }
            catch
            {
                MessageBox.Show("請選擇正確行！");
            }
            finally
            {
                // con.Dispose();      //關閉數據庫
                con.Close();
            }
            this.courseTableAdapter.Fill(this.schoolDataSet1.Course);
        }

        private void buttonchange_Click(object sender, EventArgs e)//修改
        {
            string CouCno = textBoxcno.Text.Trim();
            string CouCname = textBoxcname.Text.Trim();
            string CouCpno = textBoxcpno.Text.Trim();
            string CouCcredit = textBoxcredit.Text.Trim();
            try
            {
                con.Open();     //打開數據庫
                
                if (CouCname != "") //修改課程名稱,只能根據課程號修改
                {
                    
                    string update_cname = "UPDATE Course SET Cname='" + CouCname + "'WHERE Cno='" + CouCno + "'";
                    SqlCommand cmd = new SqlCommand(update_cname, con);
                    cmd.ExecuteNonQuery();
                }
                 if ( CouCpno != "" &&CouCno != "" || CouCname != ""&& CouCpno != "")  //修改Cpno，通過課程號修改一門課的或者通過課程名修改多門課的
                 {
                     string update_cpno = "UPDATE Course SET Cpno='" + CouCpno + "' WHERE Cno='" + CouCno + "' OR Cname='"+CouCname+"'";
                     SqlCommand cmd2 = new SqlCommand(update_cpno, con);
                     cmd2.ExecuteNonQuery();
                 }

                 if (CouCcredit != "" && CouCno != "" || CouCname != "" && CouCcredit != "")//修改Credit,通過課程號修改一門課的或者通過課程名修改多門課的
                 {
                     string update_credit = "UPDATE Course SET Ccredit='" + CouCcredit + " 'WHERE Cno='" + CouCno + "' OR Cname='"+CouCname+"'";
                     SqlCommand cmd3 = new SqlCommand(update_credit, con);
                     cmd3.ExecuteNonQuery();
                 }
               /* if (CouCpno != ""&&CouCno!="" )//根據課程號修改Cpno
                {
                    string update_cpno = "UPDATE Course SET Cpno='" + CouCpno + "' WHERE Cno='" + CouCno +"'";
                    SqlCommand cmd = new SqlCommand(update_cpno, con);
                    cmd.ExecuteNonQuery();
                }
                if (CouCpno != "" && CouCno == "" && CouCname != "")//根據課程名修改Cpno
                {
                    string update_cpno = "UPDATE Course SET Cpno='" + CouCpno + "' WHERE Cname='" + CouCname + "'";
                    SqlCommand cmd = new SqlCommand(update_cpno, con);
                    cmd.ExecuteNonQuery();
                }
                if (CouCcredit != "" && CouCno != "" )//根據課程號修改Ccredit
                {
                    string update_credit = "UPDATE Course SET Ccredit='" + CouCcredit+ "' WHERE Cno='" + CouCno + "'";
                    SqlCommand cmd = new SqlCommand(update_credit, con);
                    cmd.ExecuteNonQuery();
                }
                if (CouCcredit != "" && CouCname != "" && CouCno == "")//根據課程名修改Ccredit
                {
                    string update_credit = "UPDATE Course SET Ccredit='" + CouCcredit + "' WHERE Cname='" + CouCname + "'";
                    SqlCommand cmd = new SqlCommand(update_credit, con);
                    cmd.ExecuteNonQuery();
                }*/
            }
            catch
            {
                MessageBox.Show("輸入數據違反要求！");
            }
            finally
            {
                //con.Dispose();      //關閉數據庫
                con.Close();
            }
            this.courseTableAdapter.Fill(this.schoolDataSet1.Course);
        }

        private void buttonselect_Click(object sender, EventArgs e)//查找
        {
            string CouCno = textBoxcno.Text.Trim();
            string CouCname = textBoxcname.Text.Trim();
            string CouCpno = textBoxcpno.Text.Trim();
            string CouCcredit = textBoxcredit.Text.Trim();
            String conn = "Data Source =.; Initial Catalog = School;  Persist Security Info = True;User ID = sa; Password = 123";
            SqlConnection sqlconnection = new SqlConnection(conn);//實例化連接對象

            try
            {
                sqlconnection.Open();

                if (CouCno != "")//按照課序號查找，只有一個
                {
                    String select_by_cno = "select * from Course where Cno='" + CouCno + "'";
                    SqlCommand sqlcommand = new SqlCommand(select_by_cno, sqlconnection);
                    SqlDataReader sqldatareader = sqlcommand.ExecuteReader();
                    BindingSource bindingsource = new BindingSource();
                    bindingsource.DataSource = sqldatareader;
                    dataGridView1.DataSource = bindingsource;
                    //將讀出來的值賦給數據源，再將數據源給dataGridView
                }
                if (CouCname != "" && CouCpno == "" && CouCcredit == "")//按照課程名查找
                {
                    String select_by_cname = "select * from Course where Cname='" + CouCname + "'";
                    SqlCommand sqlcommand = new SqlCommand(select_by_cname, sqlconnection);
                    SqlDataReader sqldatareader = sqlcommand.ExecuteReader();
                    BindingSource bindingsource = new BindingSource();
                    bindingsource.DataSource = sqldatareader;
                    dataGridView1.DataSource = bindingsource;
                }
                if (CouCpno != "" && CouCname == "" && CouCcredit == "")//按照Cpno查找
                {
                    String select_by_cpno = "select * from Course where Cpno='" + CouCpno + "'";
                    SqlCommand sqlcommand = new SqlCommand(select_by_cpno, sqlconnection);
                    SqlDataReader sqldatareader = sqlcommand.ExecuteReader();
                    BindingSource bindingsource = new BindingSource();
                    bindingsource.DataSource = sqldatareader;
                    dataGridView1.DataSource = bindingsource;
                }
                if (CouCcredit != "" && CouCname == "" && CouCpno == "")//按照Credit查找
                {
                    String select_by_credit = "select * from Course where Ccredit='" + CouCcredit + "'";
                    SqlCommand sqlcommand = new SqlCommand(select_by_credit, sqlconnection);
                    SqlDataReader sqldatareader = sqlcommand.ExecuteReader();
                    BindingSource bindingsource = new BindingSource();
                    bindingsource.DataSource = sqldatareader;
                    dataGridView1.DataSource = bindingsource;
                }
                if (CouCname != "" && CouCpno != "" && CouCcredit == "")//按照Cname和Cpno查找
                {
                    String select_by_namepno = "select * from Course where Cname='" + CouCname + "' AND Cpno='"+CouCpno+"'";
                    SqlCommand sqlcommand = new SqlCommand(select_by_namepno, sqlconnection);
                    SqlDataReader sqldatareader = sqlcommand.ExecuteReader();
                    BindingSource bindingsource = new BindingSource();
                    bindingsource.DataSource = sqldatareader;
                    dataGridView1.DataSource = bindingsource;
                }
                if (CouCname != "" && CouCcredit != "" && CouCpno == "")//按照Cname和Ccredit查找
                {
                    String select_by_namecredit = "select * from Course where Cname='" + CouCname + "' AND Ccredit='" + CouCcredit + "'";
                    SqlCommand sqlcommand = new SqlCommand(select_by_namecredit, sqlconnection);
                    SqlDataReader sqldatareader = sqlcommand.ExecuteReader();
                    BindingSource bindingsource = new BindingSource();
                    bindingsource.DataSource = sqldatareader;
                    dataGridView1.DataSource = bindingsource;
                }
                if (CouCpno != "" && CouCcredit != "" && CouCname == "")//按照Cpno和Ccredit查找
                {
                    String select_by_pnocredit = "select * from Course where Cpno='" + CouCpno + "' AND Ccredit='" + CouCcredit + "'";
                    SqlCommand sqlcommand = new SqlCommand(select_by_pnocredit, sqlconnection);
                    SqlDataReader sqldatareader = sqlcommand.ExecuteReader();
                    BindingSource bindingsource = new BindingSource();
                    bindingsource.DataSource = sqldatareader;
                    dataGridView1.DataSource = bindingsource;
                }
                if (CouCname != "" && CouCpno != "" && CouCcredit != "")//按照Cname和Cpno和Ccredit查找
                {
                    String select_by_pnocreditname = "select * from Course where Cpno='" + CouCpno + "' AND Ccredit='" + CouCcredit + "' AND Cname='"+CouCname+"'";
                    SqlCommand sqlcommand = new SqlCommand(select_by_pnocreditname, sqlconnection);
                    SqlDataReader sqldatareader = sqlcommand.ExecuteReader();
                    BindingSource bindingsource = new BindingSource();
                    bindingsource.DataSource = sqldatareader;
                    dataGridView1.DataSource = bindingsource;
                }
            }
            catch
            {
                MessageBox.Show("查詢語句有誤，請認真檢查SQL語句");
            }
            finally
            {
                sqlconnection.Close();
            }
        }

        private void buttonempty_Click(object sender, EventArgs e)//清空
        {
            clear();
        }
    }
}

在寫代碼的過程中，一定要把表名和變量名寫正確，系統不會因爲表名錯誤給報錯，但是運行是錯誤的，我有的時候會因爲把名字拼錯了，把Student拼成了Studnet，找了半天才看見是名字寫錯了。