C ＃ homework - student information management system

gitee Project address

---

One 、 Database operation

Build database structure

1： Create a new database

1： open Database management software navicat/SQLoya
2： Create connection
3： Select connect and right-click to create a new database
4： Expand the database
5： Right click new table

2： The data in the table

Unique ID： Identification of this table It's like an ID card only .
id： Generally, we use it as the primary key （ Non empty 、 Self increasing ）

3： Populating data in a table

When creating a new table ： Each field has a type
When we fill in the data ： To populate data by type
int： Integers Such as ：1、2、3、…
varchar： character string ( Length... Must be specified ) Such as ：‘ stupid ’、‘ Simon blow snow ’、…

Table structure display

---

Basic operations on data ( add to modify Delete Inquire about )

Now add data to the table , Then we show the list and query

1： newly added

grammar ：INSEST INTO + Table name （ Field name 1, Field name 2, Field 3...） VALUES( list 1, list 2,...)
Return value ： Affected lines （ When adding, deleting and modifying , Will return the affected data ）

Add a new student because sid Self increasing We do not need to add a primary key every time we add data ; because sid It will automatically add .

INSERT INTO student (sname, sage) VALUES(" Zhou Zhiruo ", 19)

Add more data

INSERT INTO student (sname, sage) VALUES(' Monday ', 18),(' Tuesday ', 19),(' Wednesday ', 20)

---

2： modify

grammar ：UPDATE + Table name set Name = ' The new data ' where Conditions

hold id by 1 Name of the person Change to Zhang San

update student set sname=' Zhang San ' where sid=1

Put the name of Monday Change to Friday

update student set sname=' Sunday ' where sname=' Monday '

---

3： Delete

grammar ：DELETE from Table name + WHERE Conditions

Delete student ID as 1 Of the students

DELETE FROM student WHERE sid = 1

In real development , Deletion is not a physical deletion It's logical deletion ( That is, a variable is used to indicate whether it is deleted )

---

4： Inquire about Single table 、 Multi table query

grammar ：SELECT < Fields to query sage/sid/ All (*)> from + Table name where Conditions

Query all student information ( All the columns in the table )

SELECT * FROM student

Query student age and full name

SELECT sname, sage FROM student

Conditions of the query The age found is 18 The name of the person

SELECT sname FROM student WHERE sage=18

Multiple conditions The age of inquiry is 18 and The name is all the information about the person on Tuesday

SELECT * FROM student WHERE sage=18 AND sname=' Tuesday '

Fuzzy query Check all names with weeks

SELECT * FROM student WHERE sname LIKE '% Zhou %'

---

Why do I need to create an associated table ？

When we perform class operations , If we put the class in the student list, we may not be able to operate .
such as ： Three 2020 The students in the class , Duplicate data found in query , Another example is the addition of 2025 class , But there are no students at this time 2025 class , What if I can't operate the student list . At this time, we can consider ： Use association tables , Create a new class table .

---

C# WinForm Combined with database

Get the value of the data frame

//  According to the properties of the component name obtain   Input box (TextBox) The data in it 
// this： The current window uses  name： Property name  Text： Text 
string sname = this.sname.Text;
string sage = this.sage.Text;

The new data （ Connect to database + perform SQL sentence ）

		private void button1_Click(object sender, EventArgs e)
        {
    
            //  According to the properties of the component name obtain   Input box (TextBox) The data in it 
            // this： The current window uses  name： Property name  Text： Text 
            string sname = this.sname.Text;
            string sage = this.sage.Text;

            //  Operation of connecting database  
            // 1:  Declare a data source   Purpose ： Find my receipt bank 
            /* * server: service  localhost/127.0.0.1（ Local ） * port： Port number  MySQL The port number of the database is 3306  So it fits  * database： database   Declare which database I want to use  * uid： Database user name  * pwd: Database password  */ 
            string url = "server=127.0.0.1; port=3306;database=csharp;uid=root;pwd=root"; 
            // 2： establish   link  
            //  Be careful  :  When we link to the database, we need to reference  mysql.data.dll
            MySqlConnection con = new MySqlConnection(url); 
            // 3:  Open database 
            con.Open();
            // MessageBox.Show(" Open database ");
            //4：  Make a statement sql 
            //  since   The database has been opened   Can I perform some operations on the database 
            //  Be careful ：SQL The string needs to be enclosed in quotation marks 
            string sql = string.Format("INSERT INTO student (sname,sage) VALUES('{0}', {1})", sname, sage); 
            // 5： Create an operation  sql The object of （MySqlCommand）
            MySqlCommand com = new MySqlCommand(sql, con); 
            // 6:  After execution   Return a result   Integers  int 
            // ExecuteNonQuery:  Execute addition, deletion and modification   newly added   modify   Delete 
            int i= com.ExecuteNonQuery(); 
            if (i > 0) {
    
                // Be similar to js Medium console.log() Prompt box 
                MessageBox.Show(" Added successfully ");
            } else {
    
                MessageBox.Show(" Failure "); 
            }
        }

---

Tool class ——DBhelp encapsulation

		private static String connStr = "server=localhost;database=csharp;uid=root;pwd=root;charset=utf8;sslmode=none";
        
        // Statement link 
        public static MySqlConnection GetConn()
        {
    
            MySqlConnection conn = new MySqlConnection(connStr);//
            if (conn.State == ConnectionState.Closed) conn.Open();// Judge whether to turn off   Open the link 
            return conn;// Back to the link 
        }
        public static void CloseAll(MySqlConnection conn)
        {
    
            if (conn == null) return;
            if (conn.State == ConnectionState.Open || conn.State == ConnectionState.Connecting)
                // Judge 
                conn.Close();// Close links 
        }
        public static int ExecuteNonQuery(string sql) //  Additions and deletions   encapsulation   Returns the affected row 
        {
    
            MySqlConnection conn = null;
            int result; // Set a return value in advance 
            try
            {
    
                conn = GetConn();// For a link 
                MySqlCommand cmd = new MySqlCommand(sql, conn);
                result = cmd.ExecuteNonQuery();// perform sql  And return the number of affected rows 
            }
            finally
            {
    
                CloseAll(conn);
            }
            return result;
        }
        public static MySqlDataReader executeQuery(string sql) // Inquire about 
        {
    
            MySqlDataReader res = null;
            MySqlConnection conn = null;
            try
            {
    
                MySqlConnection conn1 = GetConn();
                MySqlCommand cmd = new MySqlCommand(sql, conn1);
                res = cmd.ExecuteReader();
            }
            finally
            {
    
                CloseAll(conn);
            }
            return res;
        }

---

Optimize new data （ Through tool class ）

		private void button1_Click(object sender, EventArgs e)
        {
    
            string sname = this.sname.Text;
            string sage = this.sage.Text;
            string sql = string.Format("INSERT INTO student (sname,sage) VALUES('{0}', {1})", sname, sage);
            int i = DBhelp.ExecuteNonQuery(sql);
            if (i > 0) {
    
                MessageBox.Show(" Added successfully ");
            } else {
    
                MessageBox.Show(" Failure "); 
            }
        }

---

Two 、 Multi meter operation

1： Why do I perform multi table operations

 As shown in the figure ： When I do class operations , There is no way to operate at this time , Monday 、 They dropped out of school on Wednesday , that 2020 This class no longer exists . Unable to operate class 2020.

2： Solution ( Create an association table , Operating multi table data )

3： Operational data

In general, multi table operations only use query operations
Multi meter operation ：as( names ) There is a problem at this time Students without classes ( namely gid by NULL) Don't Don't deserve to be inquired ？
SELECT * FROM student AS a, grade AS b WHERE a.gid = b.gid
Advanced multi table query ：INNER JOIN Internal connection LEFT JOIN Left connection ( Query with the left table as the main table If the right table has no matching data, use null Instead of )
SELECT * FROM student a LEFT JOIN grade b ON a.gid = b.gid

---

3、 ... and 、 Login operation

			//  Reset button ： Clear the value in the input box 
            this.textBox1.Text = "";
            this.textBox2.Text = "";
            this.radioButton1.Checked = true;
            this.radioButton2.Checked = false;
			
			//  Click login 
			string password = null;
            if (radioButton1.Checked == true)
            {
    
                // string.Format Formatted string 
                string sql = string.Format(@"SELECT password FROM student WHERE username='{0}'", textBox1.Text);
                //  perform sql  Return a result set 
                MySqlDataReader res = DBhelp.executeQuery(sql);
                //  Row by row   Read on 
                while (res.Read())
                {
    
                    password = res["password"].ToString();
                }
                if (password.Equals(textBox2.Text))
                {
    
                    MessageBox.Show(" Login successful ");
                } else
                {
    
                    MessageBox.Show(" Wrong account password ");
                }
            } else
            {
    
                string sql = string.Format(@"SELECT password FROM teacher WHERE username='{0}'", textBox1.Text);
                MySqlDataReader res = DBhelp.executeQuery(sql);
                while (res.Read())
                {
    
                    password = res["password"].ToString();
                }
                if (password.Equals(textBox2.Text))
                {
    
                    MessageBox.Show(" Login successful ");
                }
                else
                {
    
                    MessageBox.Show(" Account password failed ");
                }
            }

---

Four ： Menu operation

1： Show menu

					//  establish   Examples of student menus 
                    StudentMenu stu = new StudentMenu();
                    //  This is the display window 
                    stu.Show();
                    //  After showing the form , Close the previous open window 
                    this.Hide();

2：ListView Use of control

Select the edit line


modify ListView Box properties

---

5、 ... and ： Echo data

		string gid = null; // Class number 
        StuList s = null; // If it has been opened, it will no longer new 了 

        private void AddStudent_Load(object sender, EventArgs e)
        {
    
            string sql = string.Format(@"SELECT * FROM grade");
            MySqlDataReader res = DBhelp.executeQuery(sql);
            while (res.Read())
            {
    
                string gname = res["gname"].ToString();
                this.comboBox1.Items.Add(gname);
            }
            //  Set the initial value of the drop-down box 
            comboBox1.Items.Insert(0, " Please select ");
            this.comboBox1.SelectedIndex = 0;
        }

        private void button2_Click(object sender, EventArgs e)
        {
    
            string sql = string.Format(@"insert into student (sname, sage, gid, username) values('{0}', {1}, {2}, '{3}')", textBox1.Text, textBox2.Text, gid, textBox4.Text);
            int i = DBhelp.ExecuteNonQuery(sql);
            if (i > 0)
            {
    
                if (s == null)
                {
    
                    s = new StuList();
                    s.Show();
                }
                else
                {
    
                    s.Reload();
                }
                DialogResult dialogResult = MessageBox.Show(" Added successfully , Do you want to continue adding ", " New tips ", MessageBoxButtons.YesNo, MessageBoxIcon.Exclamation);
                if (dialogResult == DialogResult.Yes)
                {
    
                    this.TopMost = true;
                }
                else if (dialogResult == DialogResult.No)
                {
    
                    this.Hide();
                }
            } else
            {
    
                MessageBox.Show(" Add failed ");
            }
        }

        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
    
            // obtain gid
            string sql1 = string.Format(@"SELECT * FROM grade where gname = '{0}'", comboBox1.Text);
            MySqlDataReader res1 = DBhelp.executeQuery(sql1);
            while (res1.Read())
            {
    
                gid = res1["gid"].ToString();
            }
        }

---

6、 ... and 、 Modify delete data

Double click the event in the diagram ：

        private void listView1_SelectedIndexChanged(object sender, EventArgs e)
        {
    
            // Judge whether there is selected data , Echo data when selected 
            if (this.listView1.SelectedItems.Count > 0)
            {
    
                //  Get the selected data   Index value from 0 Start : Because one row at a time , All index values are 0
                ListViewItem lis = this.listView1.SelectedItems[0];
                string sid = lis.Tag.ToString();
                string sname = lis.Text;
                //  Get the submenu 
                string sage = lis.SubItems[1].Text;
                string gname = lis.SubItems[2].Text;
                string username = lis.SubItems[3].Text;
                // Assign the obtained data to the modification box 
                textBox1.Text = sname;
                textBox2.Text = sage;
                textBox3.Text = gname;
                textBox4.Text = username;
            }
        }

---

7、 ... and 、 Value transfer between pages

---