protected void btnCreateSemesterSubject_Click(object sender, EventArgs e) { if (string.IsNullOrWhiteSpace(ddlSemester.SelectedValue) || string.IsNullOrWhiteSpace(ddlProgramSubject.SelectedValue) || string.IsNullOrWhiteSpace(ddlLecturer.SelectedValue)) { lblSemesterSubject_Status.Text = "has empty"; } else { Semester.AssociateSemesterSubject(Convert.ToInt32(ddlSemester.SelectedValue), Convert.ToInt32(ddlProgramSubject.SelectedValue), Convert.ToInt32(ddlLecturer.SelectedValue)); lblSemesterSubject_Status.Text = "Semester subject association has been created successfully."; } }