Custom Post Type Validation without javascript

Validating content in WordPress Custom Post Types is not particularly simple in WordPress without the use of a plugin or Javascript (normally jQuery).

What I am going to show you here is how to validate input and replace the default admin message with our own error message.

Here is a very simple custom content type that contains just a title field.  I have built this as a plugin but it could just as easy be inside the theme function file.

The end product will look like this

Note that the green success message has been removed

wp-content/plugins/ddkp-music-collection.php

<?php
/*
Plugin Name: Music Collection Post Types
Plugin URI: http://kevinphillips.co.nz
Description: Learning Custom Post Types
Author: Kevin Phillips
Version: 0.1
Author URI: http://kevinphillips.co.nz
*/

/**
 * Set up the post types
 */
add_action( 'init', 
  'ddkp_music_collection_register_post_types' );

/**
 * Register music collection post types
 */
function ddkp_music_collection_register_post_types() {

  // Set up the args for the music_album post type.
  $album_args = array(
    'public' => true,
    'query_var' => 'music_album',
    'rewrite' => array(
      'slug' => 'music/album',
      'with_front' => false,
    ),
    'supports' => array( 'title', 'thumbnail '),
    'labels' => array(
    'name' => 'Albums',
    'singular_name' => 'Album',
    'add_new' => 'Add New Album',
    'add_new_item' => 'Add New Album',
    'edit_item' => 'Edit Album',
    'new_item' => 'New Album',
    'view_item' => 'View Album',
    'search_items' => 'Search Albums',
    'not_found' => 'No Album Found',
    'not_found_in_trash' => 'No Album found in trash',
  )
);
 // Register the music album post type
 register_post_type( 'music_album', $album_args );
}

As you can see I have only added support for “title” and “thumbnail”

So currently if a user adds a new “Album” and then publishes it without a title the post type will save and will give you the message “Post published. View Post” and if you look in the “All Albums” you get a post that has been published without a title. “(no title)“ 

You need to understand that WordPress is always going to save a post, regardless because that is the workflow of adding a new post, what we are going to do is add some actions and filters.

The first thing we need to do is hook into the “save_post()” function.

/**
 * Add Action save_post
 * Note that we have specified 2 arguments, 
 * these will be the post id and the post itself.
 */
add_action( 'save_post', 'album_save_post', 10, 2 );

Now lets add the function “album_save_post” with two args

/**
 * Function that will hook into save_post()
 *
 * @param int Post ID
 * @param Object the post
 * @return void
 */
function album_save_post( $album_id, $album ) {

  // First we only want music_album post types
  // and we don't want any auto saves
  if( defined('DOING_AUTOSAVE') && DOING_AUTOSAVE 
      || $album->post_type != 'music_album' ) return;

    // Setup an empty array to hold our errors.
    // Even though we are only validating one field this
    // technique can be used for multiple fields
    $errors = array();

    // Validation filters
    $title = $album->post_title;
    if ( ! $title ) {
      $errors['title'] = "The title field is required";
    }
    // You can add more validation filters here!

    // if we have errors lets setup some messages
    if ( ! empty( $errors ) ) {

      // we must remove this action or it will 
      // loop for ever @see codex
      remove_action( 'save_post', 'album_save_post' );

      // save the errors as option so we can call 
      // them back later
      update_option( 'album_errors', $errors );

      // Change post from published to draft
      $album->post_status = 'draft';

      // update the post
      wp_update_post( $album );

      // we must add back this action
      add_action('save_post', 'album_save_post');

      // admin_notice is create by a $_GET['message'] with
      // a number that wordpress uses to display the admin
      // message so we will add a filter for replacing 
      // default admin 
      // message with a redirect
      add_filter( 'redirect_post_location',
          'album_post_redirect_filter' );
    }
}

We are now going to create the function that

removes the default admin notice and replace

it with a $_GET variable that our own function

can hook onto.

/**
 * Redirect Filter
 *
 * @param array
 * @return array
 */
function album_post_redirect_filter( $location ) {
  $location = remove_query_arg( 'message', $location );

  // add our new query sting
  $location = add_query_arg( 'album', 'error', $location );

  // return the location query string
  return $location;
}

We are now going to add the custom admin notice

// Add new admin message
add_action( 'admin_notices', 
             'album_post_error_admin_message' );

/**
 * Function to add custom admin message
 */ 
function album_post_error_admin_message() {

  // Check to see if isset( $_GET['album'] )
  // we can use different values if we want
  if ( isset( $_GET['album'] ) 
        && $_GET['album'] == 'error' ) {

    // lets get the errors from the option album_errors
    $errors = get_option('album_errors');

    // now delete the option album errors
    delete_option('album_errors');

    $display = '<div id="notice" class="error"><ul>';

    // Because we are storing as an array we 
    // should loop through them
    foreach ( $errors as $error ) {
      $display .= '<li>' . $error . '</li>';
    }

    $display .= '</ul></div>';

    // finally echo out our display
    echo $display;

    // add some jQuery
    // I know I said without Javascript, all
    // this does is add red border to the
    // input field.
    // You don't need this
    ?>
    <script>
    jQuery(function($) {
      $("#title").css({"border": "1px solid red"})
    });
    </script>
    <?php
  }
}

That’s it.  You can this to any number of fields on your custom post type.