C# if certain text selected in combobox winform

Question

i have 3 combobox : cmbStatus,cmbReason,cmbTransfer, primarykey textbox txtNo_RM and the trigger button: btnAdd. Using Mysql as Database

While cmbStatus != "Transfered" cmbReason and cmbTransfer will be intended to not be selected by user. The problem is it didn't work while i use this code

private void btnAdd_Click(object sender, EventArgs e)
{
    MySqlConnection con = new MySqlConnection(MyConnectionString);
    MySqlCommand cmd;
    con.Open();
    try
    {
        cmd = con.CreateCommand();
        cmd.CommandText = "Insert Into tb_data(No_RM,Status,Reason,Transfer)Values(@No_RM,@Status,@Reason,@Transfer)";
        cmd.Parameters.AddWithValue("@NO_RM", txtNo_Rm.Text);
        cmd.Parameters.AddWithValue("@Status", cmbStatus.Text);

        if (cmbStatus.Text == "Transfered")
        {
            cmd.Parameters.AddWithValue("@Reason", cmbReason.Text);
            cmd.Parameters.AddWithValue("@Transfer", cmbTransfer.Text);
        }
        cmd.ExecuteNonQuery();


    }
    finally
    {
        if (con.State == ConnectionState.Open)
        {
            con.Close();
            LoadData();
            MessageBox.Show("Data Added!");
        }
    }



}

code above resulting fatal error message and also using SelectedText.ToString

try adding this code, resulting out of range error

if (cmbStatus.Text != "Transfered")
            {
                cmd.Parameters.AddWithValue("@Reason", "");
                cmd.Parameters.AddWithValue("@Transfer", "");
            }

thanks before

Answer 1

Use the property SelectedValue for comboboxes instead of Text . Also assign DBNull.Value or default value to the parameters @Reason and @Transfer if the cmbStatus.Text != "Transfered".

Answer 2

You can use DBValue.Null for empty values like this:

if (cmbStatus.Text == "Transfered")
{
   cmd.Parameters.AddWithValue("@Reason", cmbReason.Text);
   cmd.Parameters.AddWithValue("@Transfer", cmbTransfer.Text);
}
else
{
   cmd.Parameters.AddWithValue("@Reason", DBNull.Value);
   cmd.Parameters.AddWithValue("@Transfer", DBNull.Value);
}

Answer 3

Consider the parameterized query that you are using, it expecting four parameters as you specified in the query So you should five the four otherwise you will get that error as you described in the question; What you can do in this situation is :

cmd = con.CreateCommand();
if (cmbStatus.Text == "Transfered")
{
    cmd.CommandText = "Insert Into tb_data(No_RM,Status,Reason,Transfer)Values(@No_RM,@Status,@Reason,@Transfer)";      
    cmd.Parameters.AddWithValue("@Reason", cmbReason.Text);
    cmd.Parameters.AddWithValue("@Transfer", cmbTransfer.Text);
}
else
{
    cmd.CommandText = "Insert Into tb_data(No_RM,Status)Values(@No_RM,@Status)";         
}
cmd.Parameters.AddWithValue("@NO_RM", txtNo_Rm.Text);
cmd.Parameters.AddWithValue("@Status", cmbStatus.Text);
cmd.ExecuteNonQuery();