Multi tool use

Conversion failed when converting the varchar value 'System.Windows.Forms.ComboBox+ObjectCollection' to data type int

I began to show my DataGrid on a form is created I would like when I course id, rollno. or enroll no but when I execute this code than show the following problem:

DataGrid

id

rollno

enroll

Conversion failed when converting the varchar value 'System.Windows.Forms.ComboBox+ObjectCollection' to data type int

private void btnSubmit_Click(object sender, EventArgs e)
{
con.Open();
cmd = new SqlCommand(
"select COURSE_Id, ROLL_NO, ENROLL_NO, Sub_P_CODE, STUDENT_NA, th_a_o, th_b_o, th_c_o " +
"FROM annual_2018 " +
"where COURSE_ID = '" + course_id.Items.ToString() + "' " +
"and (ROLL_NO = '" + txtRoll.Text + "' OR ENROLL_NO = '" + TxtEnroll.Text + "')",
con);
da = new SqlDataAdapter(cmd);
dt = new DataTable();
da.Fill(dt);

Enroll_no.DataSource = dt;
con.Close();
}


1 Answer
1

You have passed the whole ComboBox, you need to specify the SelectedValue of your ComboBox. Your COURSE_ID column in the table is an int datatype and that is what you need to pass it. Also you should always use parameterized queries to avoid SQL Injection. Your code should be something like this:

ComboBox

SelectedValue

ComboBox

COURSE_ID

int selectedValue = Convert.ToInt32(course_id.SelectedValue.ToString());

cmd = new SqlCommand("select COURSE_Id, ROLL_NO, ENROLL_NO, Sub_P_CODE, STUDENT_NA," +
" th_a_o, th_b_o, th_c_o FROM annual_2018 where COURSE_ID = @courseId" +
" and (ROLL_NO = @ROLL_NO OR ENROLL_NO = @ENROLL_NO)", con);

command.Parameters.AddWithValue("@courseId", selectedValue );
//Other parameters


Although specify the type directly and use the Value property is more better than AddWithValue. See this Can we stop using AddWithValue() already?

Value

AddWithValue

cmd.Parameters.Add("@courseId", SqlDbType.Int).Value = selectedValue;


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