Validate input-fields (texbox) BEFORE execute script - php

Question

I would like to ask you, how to handle this:
Validate input-fields
if everything is OK, execute the following script which writes the fields in database
What I have till now is:
if($_SERVER['REQUEST_METHOD'] == "POST")
{
...
$checkField = "";
if (empty($_POST["tb_checkField"]))
{
$checkFieldErr = "<br> Field is required!";
}
else
{
$checkField = $_POST["tb_checkField"];
if (!preg_match("/[-a-z0-9+&##\/%?=_!:,.;]+/",$checkField))
{
$checkFieldErr = "<br> Invalid value detected!";
}
}
...
}
...
<form method="post" action="writeTodatabase.php">
<table border="0" align="center">
<tr>
<td colspan="2"><input name="tb_checkField" type="text" value="<?php echo $checkField;?>" tabindex="1" size="50" maxlength="20"/>
<span class="error"><?php echo $checkFieldErr;?></span></td>
</tr>
</table>
</form>
...
<td><p>
<input type="submit" name="submit" value="Save" tabindex="2"/>
</p></td>
So when I press the button, is directly going to execute writeTodatabase.php without checking the textbox.
So how can I tell him to go first check this values from textbox and if its ok, go and execute writeTodatabase.php?

Answer 1

Either you can choose to validate the input on the same page as the form, or you can do the validation on the writeTodatabase.php page.
The "action" parameter in the form tag decides where you want the _POST data to be sent. You can't have your validation code on the same page as the form when you're sending the _POST data to another page. You'll either have to send the data to the current page (either removing the action parameter, or changing it's value to the current page) or move the validation script to writeTodatabase.php.
If you want the validation code to remain on the current page, and remove the action parameter, you can use the header() function to redirect to writeTodatabase.php if the validation is successful. If you're gonna use the header() function remember to put the validation code at the top of the file, before any output.

Answer 2

I'm making a WEB project, and I used a form imput validations in PHP:
if($_SERVER['REQUEST_METHOD']=='POST'){
require('inc/mysqli_connect.php');
$errors=array();
/*Verifica el nombre*/
if(empty($_POST['first_name'])){
$errors[]='Verifique el campo de Nombre del participante';
}else{
$fina=mysqli_real_escape_string($dbc, trim($_POST['first_name']));
}
/*Verifica el apellido paterno*/
if(empty($_POST['ape_pat'])){
$errors[]='Verifique el campo de Apellido Paterno del participante';
}else{
$appa=mysqli_real_escape_string($dbc, trim($_POST['ape_pat']));
}
/*Verifica el apellido materno*/
if(empty($_POST['ape_mat'])){
$errors[]='Verifique el campo de Apellido Materno del participante';
}else{
$apma=mysqli_real_escape_string($dbc, trim($_POST['ape_mat']));
}
/*Verifica el genero*/
if(empty($_POST['gender'])){
$errors[]='Seleccione el Género del participante';
}else{
$gend=mysqli_real_escape_string($dbc, trim($_POST['gender']));
}
/*Verifica el correo electronico*/
if(empty($_POST['email'])){
$errors[]='Verifique el campo de Correo Electrónico del participante';
}else{
$coel=mysqli_real_escape_string($dbc, trim($_POST['email']));
}
/*and repeat the code above for all the input that you have in your form */
if(empty($errors)){
$q="INSERT INTO participante(nombre, paterno, materno, genero, correo, fechadenac, procedencia, ocupacion, asistencia, fechareg) VALUES ('$fina','$appa','$apma','$gend','$coel','$dabi','$prov','$ocup','$assi',NOW())";
$r=mysqli_query($dbc,$q);
if($r){
echo '
<p>
Nombre: <b>'.$_POST['first_name'].'</b><br />
Apellido Paterno: <b>'.$_POST['ape_pat'].'</b><br />
Apellido Materno: <b>'.$_POST['ape_mat'].'</b><br />
Genero: <b>'.$_POST['gender'].'</b><br />
Correo Electrónico: <b>'.$_POST['email'].'</b><br />
Fecha de nacimiento: <b>'.$_POST['date'].'</b><br />
Procedencia: <b>'.$_POST['provenance'].'</b><br />
Ocupación: <b>'.$_POST['ocuppation'].'</b><br />
¿Asistió? <b>'.$_POST['assistance'].'</b><br />
</p>
';
}else{
echo '
<h2><a>¡Error del Sistema!</a></h2>
<p>
El registro no pudo realizarse debido a un error del sistema. Disculpe los incovenientes.<br />
</p>
<p>
Error: '.mysqli_error($dbc).'<br />
Query: '.$q.'<br />
</p>
';
}
mysqli_close($dbc);
include ('inc/footer.html');
exit();
}else{
echo '
<p>
Revise que todo los campos hayan sido llenados correctamente.<br />
Se encontraron los siguientes errores: <br />
';
foreach ($errors as $msg) {
echo " - $msg<br />\n";
}
echo '
</p>
<p>
Ingrese los datos faltantes e intente de nuevo.
</p>
';
}
mysqli_close($dbc);
}
mysqli_connect.php has this structure:
<?php
DEFINE('DB_USER','root');
DEFINE('DB_PASSWORD','armando');
DEFINE('DB_HOST','localhost');
DEFINE('DB_NAME','flisol');
$dbc=mysqli_connect(DB_HOST,DB_USER,DB_PASSWORD,DB_NAME) OR die ('No es posible conectarse a la Base de datos: '.mysqli_connect_error());
mysqli_set_charset($dbc,'utf8');
By the way, I'm using a sticky form. Enjoy it!