hooks

Working with Arrays and Objects in Drupal with print_r() and dpm()

Submitted by Brenda Boggs
on July 1st, 2011 at 4:33:43 PM

When customizing things in Drupal, whether we like it or not, there often comes the need to dive in and alter or override things. Because of Drupal's API, we're given a lot of wonderful hooks and theme functions to take advantage of without touching Drupal core. Instead we can modify most things the way we want within our own custom module or theme, without ever having to worry about our changes getting overwritten when doing an update to our web site.

Great! There's plenty of tutorials, blog posts, forum posts and issues both on drupal.org and throughout the interwebs on how to work with data in order to bend it to our wills, but it's not always clear on how exactly to work with the data in the first place.

Understanding print_r()

PHP provides us with a handy (if not a bit "dirty") function called print_r. What it does is print readable information about PHP objects and arrays that assist with debugging and figuring out what value we're trying to target. Here is a partial output of me doing a print_r($form) in a hook_form_alter of a blog post. What we need to understand is I am printing the full output of $form, which is an array. Each piece of the array contains a key and a value, where the value can be another array, an object, or a string.

Take a look at the screenshot above. When I am manipulating this form, I need to target the keys of the array(s) in order to manipulate any of the values. Each indent shows us the tree. We know that this is printing out $form. In order to target any of the keys within that, we need to use $form['nid'] or $form['type'] or $form['uid'], and deeper than that is $form['nid']['#type'], $form['type']['#value'], or $form['uid']['#value'].

Now we understand that arrays are handled with brackets: [ ]

But PHP objects are a little different. Below is a screenshot of another part of the $form array I posted above. This portion is accessed with $form['#node']. You'll notice instead of Array, it says stdClass Object. This means we're working with an object, not an array. Let's ignore what the differences are right now, and just figure out how we manipulate that data.

Arrays are targetted with brackets. Objects are targetted with ->.

Homework: A few other useful PHP functions are var_dump() and var_export().

Using dpm()

The Devel module takes this a bit further and provides us with dpm(). This gives us output in a much more readable format, though the concept is the same.

With this, you can now use many of Drupal's great hooks to override various content-- take a look at my previous blog posts, Drupal Alters and Overrides: hook_form_alter and Drupal Alters and Overrides: hook_menu_alter.

Tags: 
6.x
7.x
drupal
hooks

Drupal Alters and Overrides: hook_form_alter

Submitted by Brenda Boggs
on September 5th, 2010 at 6:17:12 PM

One of the first rules most people coming into the world of Drupal learn, hopefully, is to not hack core. I certainly didn't know about this when I first started out and hacked to pieces a lovely Drupal 4.6 site which, amusingly enough, still exists today. Since then, though, I've become more accustomed to the various ways of altering and overriding things in both Drupal core and contrib "the Drupal way".

Because Drupal is built modular with a strong hook API system, it gives us a lot of power in terms of changing things through our own custom modules. You can read more about creating a custom module at http://drupal.org/developing/modules -- there is also a useful module with some good examples you can download from http://drupal.org/project/examples

I'm going to go through a few different ways you can alter and override content in my next series of blog posts. This first one will cover one of the most popular.

hook_form_alter

One of the most common hooks used to override or alter things in Drupal is hook_form_alter. Drupal is driven by forms-- administration settings forms, content creation forms, contact forms, menu forms, user registration forms, etc., that I don't think I've ever worked on a Drupal site where this hook wasn't used.

Let's say, for example, you've got yourself a View with some exposed filters. By default the submit button says "Apply", but you've been asked to change that to "Submit".

My custom module is called demo. If I take a look at the link above from api.drupal.org, it tells me the parameters my function should have:

hook_form_alter(&$form, &$form_state, $form_id)

This is how it would appear in my module:

function demo_form_alter(&$form, &$form_state, $form_id) {

}

I need to find the $form_id in order to make sure I'm altering only that specific form and not the others. I usually do this just by printing out $form_id. For Views exposed filters, they all have the same $form_id which is 'views_exposed_form'. In order to make sure I'm only targetting this specific exposed form, I also use the $form['#id'] value. You can get these values by doing a print_r($form) or dpm($form) in your module. My alter now looks like this:

/**
 * Implementation of hook_form_alter().
 */
function demo_form_alter(&$form, &$form_state, $form_id) {
  if ($form_id == 'views_exposed_form' && $form['#id'] == 'views-exposed-form-content-search-page-1') {
    $form['submit']['#value'] = t('Search');
  }
}

I can do all sorts of things with forms here. I can remove elements, rename them, add new ones. I can also add or override submit and validation functions. Here are a few examples:

/**
 * Implementation of hook_form_alter().
 */
function demo_form_alter(&$form, &$form_state, $form_id) {
  if ($form_id == 'views_exposed_form' && $form['#id'] == 'views-exposed-form-content-search-page-1') {
    // Rename the submit button
    $form['submit']['#value'] = t('Search');
  }
  if ($form_id == 'search_block_form') {
    // Add default "Search" text in the searchbox
    $form['search_block_form']['#default_value'] = t('Search');
  }
  if ($form_id == 'page_node_form') {
    // Remove the "Preview" option
    unset($form['buttons']['preview']);
    // Add my extra validation function
    $form['#validate'][] = 'demo_extra_validate';
  }
}
Tags: 
drupal
hooks