Check number in database

Question

In my database I have a table called "Matrices". In this table I record the livestock matrices I own on the farm, and each matrix has its respective number, which is stored in the "Number" column of the table. This column is UNIQUE in the database, so if I try to save a new matrix with the existing number, it does not save.
I was looking for a way to make my system more efficient, making it so that as soon as I typed the number to register a new matrix, it would do a search in my database and if it returned some value, block the registration, and if it does not return any value, let the matrix register continue.

Edit: I created this code:

 private void txtnumeroFocusLost(java.awt.event.FocusEvent evt) {                                    
   MatrizesDAO dao = new MatrizesDAO();
   if(dao.verificarNumero(evt.getComponent().toString())){
      JOptionPane.showMessageDialog(this.rootPane, "Numero já cadastrado");
      } else {
    }
}                     

but you’re making a mistake

Incompatible types: void cannot be converted to Boolean

Answer 1

I managed to make it work, I do not know if in the correct way. Follow the code:

DAO

public List<Matrizes> verificarNumero(String numero) {
    try {
        List<Matrizes> lista = new ArrayList<Matrizes>();

        String cmdSql = "SELECT * FROM matrizes WHERE numero LIKE ?";
        PreparedStatement stmt = conecta.prepareStatement(cmdSql);
        stmt.setString(1, numero);

        ResultSet rs = stmt.executeQuery();

        if (rs != null) {
            while (rs.next()) {
                Matrizes n = new Matrizes();
                n.setNumero(rs.getString("numero"));
                JOptionPane.showMessageDialog(null, "Numero de Matriz já cadastrado");
                NovaMatriz.txtnumero.grabFocus();
                lista.add(n);
            }
        }

        rs.close();
        stmt.close();
        return lista;
    } catch (SQLException e) {
        throw new RuntimeException(e);
    }
}  

Textfield code

 private void txtnumeroFocusLost(java.awt.event.FocusEvent evt) {                                    
    MatrizesDAO dao = new MatrizesDAO();
    String numero = txtnumero.getText();
    List<Matrizes> lista = dao.verificarNumero(numero);
}                                   

Answer 2

The simplest way to do this is to use an error handling, using a Try catch and, if an error occurs notify the user, but if the requirement is to check this while the user is editing, maybe a Focuslistener will serve:

field.addFocusListener(new FocusAdapter() {
    public void focusLost(FocusEvent e) {
        verificaValorExistenteNoBanco(e.getComponent().getText());
    }
});

Edit: While creating your screen, as soon as you add the field where the user type this number adds this Focus Listener...

field.addFocusListener(new FocusAdapter() {
    public void focusLost(FocusEvent e) {
        if(dao.verificaValorExistenteNoBanco(e.getComponent().getText())) {
            JOptioPane.showMessage(...);
        }
    }
});

Answer 3

You can implement this requirement as follows: In your text field add an event to capture the focus loss (Example here and documentation here) Or add a text field customization to support autocomplete (Examples here)