Validate form in functions.php, send errors back to template

Question

I have a form in a template that upon submission should be validated, and any errors should be displayed, and if no errors, insert the data into the database.

I'm new to wordpress, but my idea was that maybe an "action" could solve this. So I have a function in functions.php:

    function signup_validate_insert($errors){
       if (isset($_POST['submit_msg'])) {

             // validate , insert into database

        }
    return $errors;
}

and I have the "add action" on the functions.php:

add_action('signup_insert', 'signup_validate_insert');

The form is actually in a template part which is added to a template page (with " get_template_part").

In the template part I have added the action:

<?php do_action('signup_insert', $errors); ?>

The form is sent to the same page on submit.

There is a div for displaying errors:

<div class="errors">
    <?php if((isset($errors))){

        foreach($errors as $error): ?>
            <p class='errortext'> <?php $error ?> </p>
        <?php endforeach ?>
    <?php }else if(!isset($errors)){

    } ?>
</div>

The action function registers that "$_POST" is set on submit. But it doesn't return the "$errors" array, because I get "Undefined variable: errors" in my form page. So I wonder how I get this function to return this variable?

Answer 1

You need a filter not an action. Something like this (notes are commented into the code. You have a few PHP errors that you need to correct):

function signup_validate_insert($post){
  $errors = false;
  if (isset($post['submit_msg'])) {
    // validate , insert into database
  }
  return $errors;
}
add_filter('signup_insert', 'signup_validate_insert');
$errors = apply_filters('signup_insert', $_POST);

if((!empty($errors))){ // $errors is going to be set; use empty() ?>
  <div class="errors"><?php 
    foreach($errors as $error) { ?>
      <p class='errortext'><?php 
        echo $error; // echo was missing; you would have no output ?> 
      </p><?php 
    } ?>
  </div><?php
}

Filters return content. Actions do stuff. I you want an action echo directly from your callback:

function signup_validate_insert($post){
  $errors = false;
  if (isset($post['submit_msg'])) {
    // validate , insert into database
  }
  if((!empty($errors))){ // $errors is going to be set; use empty() ?>
    <div class="errors"><?php 
      foreach($errors as $error) { ?>
        <p class='errortext'><?php 
          echo $error; // echo was missing; you would have no output ?> 
        </p><?php 
      } ?>
    </div><?php
  }
}
add_action('signup_insert', 'signup_validate_insert');
do_action('signup_insert', $_POST);

Honestly, what you are doing may be overly complicated and the whole thing might best be written without the hook at all. Do you need this to be extensible by a third party?

Try looking over: Clarification on filters and hooks Difference Between Filter and Action Hooks?