C summary of knowledge points 3

1. Database connection steps ：Connection object

//1. Construct connection string

string strconn = "Data Source=.;Initial Catalog=studentInf;Integrated Security=True";

//2. Construct connection objects

 SqlConnection s = new SqlConnection(strconn);

//try To prevent abnormalities

try

{

//3. Open the connection

s.Open();

MessageBox.Show(" Database open ");

}

// If there is an exception, it will be displayed

catch (Exception ex)

{

MessageBox.Show(ex.Message);

}

// Database shutdown

finally

{

s.Close();

MessageBox.Show(" Database shutdown ");

}

2. Database operation ：Command object - Login box connection database

1. Database connection

string strconn = "Data Source=.;Initial Catalog=studentInf;Integrated Security=True";

SqlConnection conn = =new SqlConnection(strconn);

// Receive the input user name in the text box 、 password ：

 string name = txtUserName.Text;

 string pwd = txtUserPwd.Text;

  try

  {

conn.Open();

2. Definition SQL sentence

string sqlstr=string.Format("select * from tb_User where UserName='{0}' and UserPasswd='{1}'",name,pwd);

3. establish Command The object of // Encapsulates all operations on external data sources （ Include add delete change check ）

Method 1

SqlCommand comm = newSqlCommand();

comm.Connection = conn;//Connection Property settings get Command Object used Connection object

comm.CommandText = sqlstr;//CommandText Property is used to set or get the SQL sentence

Method 2

SqlCommand comm2 = newSqlCommand(sqlstr, conn);

// Execute the query ,

if (comm.ExecuteScalar() == null)// ExecuteScalar() Method to execute the query , And return the query results. The first row and the first column in the query result set （object type ）, Return if not found null

{

      MessageBox.Show(" User name and password do not match , Login failed ");

     }

     else

     {

      // Login to another with the correct password framain Main form page

 frmMain frmmain = newfrmMain();

 frmmain.Show();// Show main window

}

}

catch (Exception ex)// Abnormal display appears

{

MessageBox.Show(ex.Message);

}

finally

{

conn.Close();// Close database connection

}

}

3 Then add information to the database in the form

string conn = "Data Source=.;Initial Catalog=studentInf;Integrated Security=True";

SqlConnection a = newSqlConnection(conn);

if (txtCollegeNo.Text == "" || txtCollegeName.Text == "")// Determine whether the form input box is empty

{

MessageBox.Show(" Department number or department name cannot be empty ");

}

else

{

try

{

1. Open();// Database open

// add to SQL sentence

string sqlstr = string.Format("insert into tb_College values('{0}','{1}')", txtCollegeNo.Text, txtCollegeName.Text);

//Command object

SqlCommand comm = newSqlCommand();

comm.Connection = a;

comm.CommandText = sqlstr;

int result = comm.ExecuteNonQuery();// perform ExecuteNonQuary Method returns a int value , The return value is the number of lines affected by the command

if (result != 0)

{

MessageBox.Show(" Insert the success ");

}

else

{

MessageBox.Show(" insert ? Enter into ¨? loss º¡ì Defeat 㨹");

}

}

catch (Exception ex)

{

// Display exception

MessageBox.Show(ex.Message);

}

finally

{

a.Close();// Database shutdown

}

4. Enter the Department query information , And display in the form box

string conn = "Data Source=.;Initial Catalog=studentInf;Integrated Security=True";

SqlConnection a = newSqlConnection(conn);

try

{

1. Open();

// Query statement

string sqlstr = string.Format("select * from tb_College where DepartmentID='{0}'", txtCollegeNo.Text);

SqlCommand comm = newSqlCommand();

comm.Connection = a;

comm.CommandText = sqlstr;

// establish DataReader object ,DataReader Objects cannot be instantiated directly with constructors , Must pass Command Object's ExecuteReader（） Method to generate .

SqlDataReader read = comm.ExecuteReader();

if (read.Read())// call Read（） Method , Find out

{

// Put the second column of data queried in txtCollegeName The box displays

txtCollegeName.Text = read[1].ToString();

}

else

{

// If the query cannot find the output

MessageBox.Show(" The query result does not exist ");

txtCollegeName.Text = "";// Clear query results

}

}

catch (Exception ex)

{

MessageBox.Show(ex.Message);

}

finally

{

a.Close();

}

4. Delete the queried data

DBhelp Is a help class , Can be called directly

try

{

DBhelp.conn.Open();

//SQL Delete statements

string sqlstr = string.Format("delete from tb_College where DepartmentID='{0}'and DepartmentName='{1}' ", txtCollegeNo.Text, txtCollegeName.Text);

DBhelp.comm.CommandText = sqlstr;

DBhelp.comm.Connection = DBhelp.conn;

if ((int)DBhelp.comm.ExecuteNonQuery() > 0)// call Command object ExecuteNonQuery() Method returns the number of affected rows

{

MessageBox.Show(" Delete successful ");

}

else

{

MessageBox.Show(" Delete failed ");

}

}

catch (Exception ex)

{

// Display exception

MessageBox.Show(ex.Message);

}

finally

{

// Close database connection

DBhelp.conn.Close();

}

5. Use the form to update the database

…