private void button1_Click(object sender, EventArgs e) { string fName = null; string lName = null; string sName = null; int? wExp = null; int? pos = null; try { fName = textBox1.Text; lName = textBox2.Text; sName = textBox3.Text; wExp = Convert.ToInt32(textBox4.Text); var posResult = DBConnectionService.SendScalarQueryToSqlServer($"select id from position where name='{comboBox1.Text}'"); if (posResult == null) { throw new Exception("\"Position\" value is not correct"); } else { pos = Convert.ToInt32(posResult); } } catch (Exception exc) { MessageBox.Show(exc.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error); return; } string query = "insert into teacher (first_name, last_name, sur_name, degree_id, position_id, work_expirience)" + "values (" + $"'{fName}','{lName}','{sName}',null,{pos},{wExp}" + ")"; int?result = DBConnectionService.SendCommandToSqlServer(query); if (result != null && result > 0) { MessageBox.Show("Done", "Saving object", MessageBoxButtons.OK, MessageBoxIcon.Information); this.Close(); } }