PHP multiple page form validation

Question

This is a tricky question to phrase so I'll try my best. I'm a noob and have little knowledge of php so be kind :D

I want to validate forms on a page that is a form handler, so for example my first page with the form (taken from w3schools):

<form action="welcome.php" method="post">
Name: <input type="text" name="name"><br>
E-mail: <input type="text" name="email"><br>
<input type="submit">
</form>

</body>
</html>

So 'welcome.php' is my 'POST' form handler page. But on this page I also want more forms, and on this page I want to validate the forms on it. Say for example some form like:

 <form method="post" action='?php echo        htmlspecialchars($_SERVER["PHP_SELF"]);?>'>
 <input type ="text" name="newBalance"><span class="error">*<?php echo    $balanceErr;?></span>
 </form>

So i would have some php validation like:

if ($_SERVER["REQUEST_METHOD"] == "POST") {
  if (empty($_POST["newBalance"])) {
    $balanceErr = "Balance is required";
  } else {
     $balance = test_input($_POST["newBlance"]);
     // check if name only contains letters and whitespace
      if (!preg_match("/^[a-zA-Z ]*$/",$name)) {
      $balanceErr = "Only letters and white space allowed"; 
   }
 }

...and so on.

Problem is as soon as I enter this page it validate form directly from the previous page and error shows for empty fields on page. Is there some way to avoid this or so I need a new approach?

Store values to Database and then echo them from DB on welcome.php? — Pavel Janicek
– Pavel Janicek, Commented May 10, 2016 at 10:52
If the validation checks out I'm storing them in a database, I don't want to write to a database until after an error check. — oodes
– oodes, Commented May 10, 2016 at 10:56
Add another submit button with a name to your second form. Than - first check if button was clicked and than check your condition (empty($_POST["newBalance"])) — Tomasz Buczeń
– Tomasz Buczeń, Commented May 10, 2016 at 10:56
Yes I like the sound of this. I already have the second button. So would this be correct.... inside the validation loop have if ( isset( $_POST['Submit_button_2'] ) ) { execute validation} ?? — oodes
– oodes, Commented May 10, 2016 at 11:02
You won't need to set the form action if it submits to itself :) — Cas
– Cas, Commented May 10, 2016 at 11:10

Gopal Joshi · Accepted Answer · 2016-05-10 11:15:15Z

As i understand your issue, you need to check first that which form submitted in validation snippet.

Insert new hidden field in second form and when you validate newBalance field, check if action is set or not. action field will just set when form2 submitted.

Here is code can help you out.

welcome.php

// Form2
<form method="post">
    <input type ="text" name="newBalance"><span class="error">*<?php echo    $balanceErr;?></span>
    <input type ="hidden" name="action" value="true" />
</form>

Validation

if ($_SERVER["REQUEST_METHOD"] == "POST" and isset($_POST['action'])) {
  if (empty($_POST["newBalance"])) {
    $balanceErr = "Balance is required";
  } else {
     $balance = test_input($_POST["newBlance"]);
     // check if name only contains letters and whitespace
     if (!preg_match("/^[a-zA-Z ]*$/",$name)) {
         $balanceErr = "Only letters and white space allowed"; 
     }
}

May above code helps you.

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