我怎样才能让我的项目占用一列，以便我可以使用它插入另一个 window 的值和 select 来自

Question

let me explain the idea of my simple project so you can get my question.. I have a multi login page first page is student and the other admin in the login page the values are set as select from and in the student it is set as insert into so the problem is the student will enter his window and make a request and it will go back to the database but the problem that i'm facing now i can't tell which student made the request. i need somehow to take the column username from the login table which is set as select from and make it into the insert into in the student table ! i have no idea how to do that but i hope you get my question i will put the coding for the reference and excuse my rookie question and coding .

 if (sqlCon.State == ConnectionState.Closed)
                sqlCon.Open();
                string query = "SELECT count (1) FROM Login WHERE Username=@Username AND password=@password AND usertype=@usertype";
            SqlCommand sqlCmd = new SqlCommand(query, sqlCon);


            sqlCmd.CommandType = CommandType.Text;
            sqlCmd.Parameters.AddWithValue("@Username", txtUsername.Text);
            sqlCmd.Parameters.AddWithValue("@password", txtPassword.Text);
            if (checkbox1.IsChecked == true)
            sqlCmd.Parameters.AddWithValue("@usertype", checkbox1.Content.ToString());
            else if (checkbox2.IsChecked == true)
                sqlCmd.Parameters.AddWithValue("@usertype", checkbox2.Content.ToString());
            int count = Convert.ToInt32(sqlCmd.ExecuteScalar());
            if (count == 1)

            {
                if ((bool)checkbox1.IsChecked == true)
                {

                    MainWindow Dashboard = new MainWindow();
                    Dashboard.Show();
                    MessageBox.Show("You're logged in as an Admin");


                    this.Close();
                }

                if ((bool)checkbox2.IsChecked == true)
                {

                    Student stu = new Student();
                    stu.Show();
                    MessageBox.Show("You're logged in as a Student");
                    this.Close();
                 }
            }

///the Student window

  private void button_Click(object sender, RoutedEventArgs e)
    {

        using (var Con = new SqlConnection(@"Data Source = test\SQLEXPRESS; Initial Catalog =Log-In; Integrated Security = True"))
        {
            Con.Open();
            var table = "INSERT INTO  Student(DepartureCiry,ArrivalCity,DateOfDeparture,DateOfReturn)VALUES(@DepartureCiry,@ArrivalCity,@DateOfDeparture,@DateOfReturn)";
            using (var cmd = new SqlCommand(table, Con))
            {
                cmd.Parameters.AddWithValue("@DepartureCiry", fromtxt.Text);
                cmd.Parameters.AddWithValue("@ArrivalCity", Totxt.Text);
                cmd.Parameters.AddWithValue("@DateOfDeparture", date_time_picker.Text);
                cmd.Parameters.AddWithValue("@DateOfReturn", date_time_picker1.Text);
                cmd.ExecuteNonQuery();
                MessageBox.Show("Data inserted suckssfully");

Answer 1

You need to change your query to be

string query = "SELECT Username FROM Login WHERE Username=@Username AND password=@password AND usertype=@usertype";

Instead of selecting only the count(1) you select the actual row (in my case I only select the Username column as you only need it).

Then instead of calling ExecuteScalar on the sql command you need to use a SqlDataReader to actually retrieve the row.

        SqlDataReader reader = sqlCmd.ExecuteReader();
        if (reader.HasRows)
        {
            string userName;
            while (reader.Read())
            {
                userName = ((IDataRecord)reader)["Username"].ToString();
                break;
            }
        }

From here you have your student name from the Login table. However my observation is that this name will actually be the same as the txtUsername.Text . I think you need some other columns from the Students table, but generally this is the way to retrieve them - user SqlDataReader , and retrieve the column with the ((IDataRecord)reader)["MyColumnName"] .

Some additional notes: I use HasRows property on the reader to see if it has a match instead of getting the count. And I imply that you have unique Usernames in the database (otherwise you have to loop the reader to see how many rows it return).