private void button1_Click(object sender, EventArgs e) { using (var ctx = new ScheduleContext()) { if (comboBox1.SelectedItem.ToString() == "" || comboBox2.SelectedItem.ToString() == "" || comboBox3.SelectedItem.ToString() == "") { MessageBox.Show("Missing required input from dropdown menu.", "Missing input", MessageBoxButtons.OK, MessageBoxIcon.Error); } else { int groupId = Convert.ToInt32(comboBox1.SelectedValue); int courseId = Convert.ToInt32(comboBox2.SelectedValue); int professorId = Convert.ToInt32(comboBox3.SelectedValue); if (ctx.GroupCourseProfessors.Any(gcp => gcp.GroupId == groupId && gcp.CourseId == courseId && gcp.ProfessorId == professorId)) { this.Close(); return; } var g = new GroupCourseProfessor { GroupId = groupId, CourseId = courseId, ProfessorId = professorId, Timeslots = Convert.ToInt32(textBox1.Text) }; ctx.GroupCourseProfessors.Add(g); ctx.SaveChanges(); this.Close(); } } }