Jul 05 2014
Jul 05

How to Build a Drupal 8 Module

Even though Drupal 7 core fell short of a proper way of handling its brand new entity system (we currently rely on the great Entity module for that), it did give us EntityFieldQuery. For those of you who don’t know, EntityFieldQuery is a very powerful querying class used to search Drupal entities programatically (nodes, users, etc).

It provides a number of methods that make it easy to query entities based on conditions such as field values or class properties. If you don’t know how it works, feel free to check out this documentation page or this great tutorial on the subject.

In this article I am going to talk about what we have in Drupal 8 for querying entities. There is no more EntityFieldQuery, but there’s an entity.query service that will instantiate a query object for a given entity type (and that implements the \Drupal\Core\Entity\Query\QueryInterface). We can access this service statically through the \Drupal namespace or using dependency injection.

First up, we’ll look at querying node entities and then we’ll see how to load them. The same techniques will work with other content entities as well (users, comments etc), but also with configuration entities, and that’s really cool.

The entity query service

As mentioned, there are two ways we can access the entity.query service that we use for querying entities. Statically, we can do this:

$query = \Drupal::entityQuery('node');

Instead of node, we can specify any other entity type machine name and what we get inside the $query variable is the query object for our entity type. The entityQuery() static method on the \Drupal namespace is a shortcut for doing so using the entity.query service.

Alternatively (and the highly recommended approach) is to use dependency injection.

If you have access to the container, you can load the service from there and then get the right query object:

$entity_query_service = $container->get('entity.query');
$query = $entity_query_service->get('node');

As you can see, we use the get() method on the entity_query service to instantiate a query object for the entity type with the machine name passed as a parameter.

Querying entities

Let’s illustrate a couple of examples of querying for node entities using this object.

A very simple query that returns the published nodes:

$query = \Drupal::entityQuery('node')
    ->condition('status', 1);
    
$nids = $query->execute();

$nids will be an array of entity ids (in our case node ids) keyed by the revision ids (if there is revisioning enabled for the entity type) or the entity ids if not. Let’s see an example in which we add more property conditions as well as field conditions:

$query = \Drupal::entityQuery('node')
    ->condition('status', 1)
    ->condition('changed', REQUEST_TIME, 'condition('title', 'cat', 'CONTAINS')
    ->condition('field_tags.entity.name', 'cats');

$nids = $query->execute();

In this query, we retrieve the node ids of all the published nodes that have been last updated before the current time, that have the word cat inside their title and that have a taxonomy term called cats as a reference in the field_tags.

As you can see, there is no more distinction between propertyCondition and fieldCondition (as there is in D7 with EntityFieldQuery). Additionally, we can include conditions based on referenced entities tacking on the entity.(column) to the entity reference field name.

An important thing to note is that we also have the langcode parameter in the condition() method by which we can specify what translation of the node should be included in the query. For instance, we can retrieve node IDs that contain a specific value inside of a field in one language but another value inside the same field for another language.

For more information on the condition() method you should consult the API documentation.

The next thing we are going to look at is using condition groups (both AND and OR) for more powerful queries:

$query = \Drupal::entityQuery('node')
    ->condition('status', 1)
    ->condition('changed', REQUEST_TIME, 'orConditionGroup()
    ->condition('title', 'cat', 'CONTAINS')
    ->condition('field_tags.entity.name', 'cats');

$nids = $query->condition($group)->execute();

Above, we altered our previous query so as to retrieve nodes that either have the cat string in their title or have a reference to the term called cats in their field_tags field. And we did so by creating an orConditionGroup object that we then pass to the query as a condition. And we can group together multiple conditions within a andConditionGroup as well.

There are many other methods on the QueryInterface that can extend the query (such as for sorting, range, etc). I encourage you to check them out in the documentation and experiment with them. For now, though, let’s take a quick look at what to do with the result set.

Loading entities

As I mentioned above, the execute() method on the query object we’ve been working with returns an array of entity IDs. Supposedly we now have to load those entity objects and work with them. How do we do that?

In Drupal 7 we had the entity_load() function to which we passed an array of IDs and that would return an array of objects. In Drupal 8, this helper function is maintained and you can use it pretty much in the same way, except only for one entity at a time:

$node = entity_load('node', $nids[1]);

And the return value is a node object. To load multiple nodes, you can use the entity_load_multiple() function:

$nodes = entity_load_multiple('node', $nids);

Which then returns an array of entity objects keyed by their ids.

A bonus nugget of information is that both of these functions are wrappers for the storage manager of the entities in question. They basically retrieve the storage manager statically and then call the load() and loadMultiple() methods, respectively, on it:

Statically, you could do similarly:

$node_storage = \Drupal::entityManager()->getStorage('node');

// Load multiple nodes
$node_storage->loadMultiple($ids);
// Load a single node
$node_storage->load($id);

But better yet, you could use dependency injection and retrieve the storage class from the container:

$node_storage = $container->get('entity.manager')->getStorage('node');

And then proceed with the loading. Using dependency injection is usually the recommended way to go when it’s possible, i.e. when working within a class. This makes it easier to test your class and better decouples it from the rest of the application.

Conclusion

In this article we’ve seen how to work with querying and loading entities in Drupal 8. There has been an overhaul of the D7 EntityFieldQuery class that turned into a robust API for querying both content and configuration entities. We’ve looked at querying content entities but the system works just the same with config entities. And that is a bit of a win for the new Drupal 8 entity system.

We’ve also seen how to load entities based on the IDs resulted in these queries and what is actually behind the wrapper functions that perform these operations. Next up, we are going to look at defining our own content entity type in Drupal 8. For a refresher on how we do it in Drupal 7, you can check out these Sitepoint articles on the subject.

Jun 23 2014
Jun 23

In this article we will continue exploring the powers of Views and focus on how to use relationships, contextual filters and rewrite field outputs. In a previous tutorial I showed you how to create a new View and perform basic customizations for it. We’ve seen how to select a display format, which fields to show and how to filter and sort the results.

In this article we will go a bit further and see what relationships and contextual filters are – the two most important options found under the Advanced fieldset at the right of the View edit page. Additionally, we’ll rewrite the output of our fields and combine their values into one.

To begin with, I have a simple article View that just shows the titles. Very easy to set up if you want to follow along. And there are three things I want to achieve going forward:

  1. Make it so that the View shows also the username of the article author
  2. Make is so that the View shows only articles authored by the logged in user
  3. Make it so that the author username shows up in parenthesis after the title

Relationships

First, let’s have the View include the author of the articles. If the View is displaying fields (rather than view modes or anything else), all we have to do is find the field with the author username, right? Wrong. The problem is the following: the node table only contains a reference to the user entity that created the node (in the form of a user ID – uid). So that’s pretty much all we will find if we look for user related fields: Content: Author uid.

What we need to do is use a relationship to the user entity found in the user table. Relationships are basically a fancy way of saying that table A (in our case node) will join with table B (in our case user) in order to retrieve data related to it from there (such as the name of the user and many others). And the join will happen in our case on the uid field which will match in both tables.

So let’s go ahead and add a new relationship of the type Content: Author. Under Identifier, we can put a descriptive name for this relationship like Content Author. The rest we can leave as default.

Now if you go and add a new field, you’ll notice many others that relate to the user who authored the content. Go ahead and add the User: Name field. In its settings, you’ll see a Relationship select list at the top where the relationship identifier we just specified is automatically selected. That means this field is being pulled in using that relationship (or table join). Saving the field will now add the username of the author, already visible in the View preview.

relationships

You can also chain relationships. For instance, if the user entity has a reference to another table using a unique identifier, you can add a second relationship. It will use the first one and bring in fields from that table. So the end result will be that the View will show fields that relate to the node through the user who authored the node but not strictly from the user table but somewhere else connected to the author. And on and on you can join tables like this.

Contextual filters

Contextual filters are similar to regular filters in that you can use mainly the same fields to filter the records on. Where contextual filters differ greatly is that you do not set the filtering value when you create the View, but it is taken from context.

There are many different contexts a filter value can come from, but mainly it comes from the URL. However, you can instruct Views to look elsewhere for contexts as well – such as the ID of the logged in user.

What we’ll do now is add a contextual filter so that the View shows only the articles authored by the logged in user. So go ahead and add a new contextual filter of the type Content: Author uid. Next, under the WHEN THE FILTER VALUE IS NOT IN THE URL fieldset, select the Provide default value radio. Our goal here is to have Views look elsewhere if it does not find the user ID in the URL.

contextual filters

You then have some options under the Type select list, where you should choose User ID from logged in user. This will make Views take the ID of the user that is logged in and pass it to the View as a filter. The rest you can leave as is and save the filter. You’ll immediately notice in your preview that only articles authored by you show up. The filtering is taking place dynamically. If you log in with another user account, you should see only the articles authored by that user account.

A great thing about contextual filters is that if you are displaying a View programatically in a custom module, you can pass the filtering value in code, which opens the door to many possibilities.

Rewriting fields

The last thing we will do in this tutorial is look at rewriting fields in order to concatenate their values. We will illustrate this technique by changing the title field to include the author username in parenthesis.

We’ll start by rearranging the order of the fields and move the title to be the last one showing. The reason we want to do this is that when you rewrite fields, you can use tokens that get values only from fields that are added before the one being rewritten. And since we want to rewrite the title field, we want the token for the username value to be present so we need to move it before the title field.

Now that the title field is last, edit the author username field and uncheck the box Create a label and then check the box Exclude from display. You can now save the field. The reason we are excluding this field from being displayed in our View is so that we don’t duplicate it once we concatenate it to the title field.

rewriting fields

Next, edit the title field and under REWRITE RESULTS, check the box Rewrite the output of this field. A new textarea should appear below where we will write the new contents of this field. If you write some gibberish in there and save the field, you’ll notice the title gets replaced by that gibberish.

Below this textarea, you’ll notice also some REPLACEMENT PATTERNS. These represent tokens of all the fields in the View loaded before this one (and including this one as well). So if you followed along, you’ll see there [name] and [title], among others.

What we need to do now is put these tokens in this box, wrapped with the text or markup we want. Having said that we want the username to be in parenthesis after the node title, we can add the following to the text box to achieve this:

[title] ([name])

Save the field and check out the result. Now you should have the author user in parenthesis. However, it’s still not perfect. We left the title field’s Link this field to the original piece of content box checked and this is breaking the output for us a bit due to also the username having a link to the user profile page. What we want is a clean link to the node title and in parenthesis (which themselves do not link to anything), the username linking to the user profile page.

So first up, add a new field called Content: Path (the path to the node). Make sure you exclude it from display, remove its label and move it before the title field. Then, edit the title field, uncheck the Link this field to the original piece of content box and replace the REWRITE RESULTS text with this:

 href="[path]">[title] ([name])

The [path] token is available from the new field we just added. And after you save, you should see already in the preview a much cleaner display of title nodes and usernames in parenthesis.

Conclusion

In this tutorial we’ve looked at three main aspects of building Views in Drupal 7: relationships, contextual filters and rewriting fields. We’ve seen how with the use of relationships we can use information also from related entities, not just those on the base table a View is built on. Contextual filters are great for when the View needs to display content dynamically depending on various contextual conditions (such as a URL or logged-in user). Lastly, we’ve learned how to rewrite fields and build more complex ones with values taken from multiple fields. As you can see, this technique is very powerful for theming Views as it allows us to output complex markup.

Views is pretty much the most popular Drupal module and it is highly complex. Despite its complexity, building views as a site administrator is very easy. All you need to understand is a few basic concepts and you are good to go. Developing for Views to extend its functionality or expose data to it is also an enjoyable experience. If you’d like to know more about that, you can read my tutorial on exposing your own custom module table to Views right here on Sitepoint.com.

Jun 18 2014
Jun 18

How to Build a Drupal 8 Module

In the previous article on Drupal 8 module development, we’ve looked at creating block types and forms. We’ve seen that blocks are now reusable and how everything we need to do for defining block types happens in one single class. Similarly, form generation functions are also grouped under one class with specific methods performing tasks similar to what we are used to in Drupal 7.

In this tutorial, I will continue where we left off. I will illustrate how we can turn our DemoForm into a form used to store a value through the Drupal 8 configuration system. Following that, we will talk a bit about the service container and dependency injection by way of illustration.

Don’t forget that you can check out this repository if you want to get all the code we write in this tutorial series.

When we first defined our DemoForm, we extended the FormBase class which is the simplest implementation of the FormInterface. However, Drupal 8 also comes with a ConfigFormBase that provides some additional functionality which makes it very easy to interact with the configuration system.

What we will do now is transform DemoForm into one which will be used to store the email address the user enters. The first thing we should do is replace the extended class with ConfigFormBase (and of course use it):

use Drupal\Core\Form\ConfigFormBase;

class DemoForm extends ConfigFormBase {

Before we move on to changing other things in the form, let’s understand a bit how simple configuration works in Drupal 8. I say simple because there are also configuration entities that are more complex and that we will not cover today. As it stands now, configuration provided by modules (core or contrib) is stored in YAML files. On enabling a module, this data gets imported into the database (for better performance while working with it). Through the UI we can change this configuration which is then easily exportable to YAML files for deployment across different sites.

A module can provide default configuration in a YAML file located in the config/install folder in the module root directory. The convention for naming this file is to prefix it with the name of the module. So let’s create one called demo.settings.yml. Inside this file, let’s paste the following:

demo:
  email_address: [email protected]

This is a nested structure (like an associative array in PHP). Under the key demo, we have another key|value pair. And usually to access these nested values we use a dot(.). In our case demo.email_address.

Once we have this file in place, an important thing you need to remember is that this file gets imported only when the module is installed. So go ahead and reinstall it. And now we can turn back to our form and go through the methods that need adapting one by one.

This is how the buildForm() method should look like now:

public function buildForm(array $form, array &$form_state) {
  
  $form = parent::buildForm($form, $form_state);
  
  $config = $this->config('demo.settings');
  
  $form['email'] = array(
    '#type' => 'email',
    '#title' => $this->t('Your .com email address.'),
    '#default_value' => $config->get('demo.email_address')
  );
  
  return $form;
}

First of all, as opposed to FormBase, the ConfigFormBase class implements this method as well in order to add elements to the form array (a submit button). So we can use what the parent did before adding our own elements.

Now for the configuration part. Drupal 8 provides a Config object that we can use to interact with the configuration. Some classes already have it available through dependency injection. ConfigFormBase is one such class.

As you can see, we are using the config() method of the parent class to retrieve a Config object populated with our demo.settings simple configuration. Then, for the #default_value of the email form element, we use the get() method of the Config object to retrieve the value of the email address.

Next, we only need to change the submit handler because the validateForm() method can stay the same for now:

public function submitForm(array &$form, array &$form_state) {
  
  $config = $this->config('demo.settings');
  $config->set('demo.email_address', $form_state['values']['email']);
  $config->save();
  
  return parent::submitForm($form, $form_state);
}

In this method we first retrieve the Config object for our configuration (like we did before). Then, we use its set() method to change the value of the email_address to the value the user submitted. Then we use the save() method to save the configuration. Lastly, we extend the parent submit handler because it does contain some functionality (in this case it sets a Drupal message to the screen).

And that’s pretty much it. You can clear the cache and try it out. By submitting a new email address, you are storing it in the configuration. The module demo.settings.yml file won’t change of course, but you can go and export the demo.settings configuration and import it into another site.

The service container and dependency injection

The next thing we are going to look at is the service container. The idea behind services is to split functionality into reusable components. Therefore a service is a PHP class that performs some global operations and that is registered with the service container in order to be accessed.

Dependency injection is the way through which we pass objects to other objects in order to ensure decoupling. Each service needs to deal with one thing and if it needs another service, the latter can be injected into the former. But we’ll see how in a minute.

Going forward, we will create a very simple service and register it with the container. It will only have one real method that returns a simple value. Then, we will inject that service as a dependency to our DemoController and make use of the value provided by the service.

In order to register a service, we need to create a demo.services.yml file located in the root of our module, with the following contents:

services:
    demo.demo_service:
        class: Drupal\demo\DemoService

The file naming convention is module_name.services.yml.

The first line creates an array of services. The second line defines the first service (called demo_service, prefixed by the module name). The third line specifies the class that will be instantiated for this service. It follows to create the DemoService.php class file in the src/ folder of our module. This is what my service does (nothing really, it’s just to illustrate how to use it):

<?php

/**
 * @file
 * Contains Drupal\demo\DemoService.
 */

namespace Drupal\demo;

class DemoService {
  
  protected $demo_value;
  
  public function __construct() {
    $this->demo_value = 'Upchuk';
  }
  
  public function getDemoValue() {
    return $this->demo_value;
  }
  
}

No need to explain anything here as it’s very basic. Next, let’s turn to our DemoController and use this service. There are two ways we can do this: accessing the container globally through the \Drupal class or use dependency injection to pass an object of this class to our controller. Best practice says we should do it the second way, so that’s what we’ll do. But sometimes you will need to access a service globally. For that, you can do something like this:

$service = \Drupal::service('demo.demo_service');

And now $service is an object of the class DemoService we just created. But let’s see how to inject our service in the DemoController class as a dependency. I will explain first what needs to be done, then you’ll see the entire controller with all the changes made to it.

First, we need access to the service container. With controllers, this is really easy. We can extend the ControllerBase class which gives us that in addition to some other helpers. Alternatively, our Controller can implement the ContainerInjectionInterface that also gives us access to the container. But we’ll stick to ControllerBase so we’ll need to use that class.

Next, we need to also use the Symfony 2 ContainerInterface as a requirement of the create() method that instantiates another object of our controller class and passes to it the services we want.

Finally, we’ll need a constructor to get the passed service objects (the ones that create() returns) and assign them to properties for later use. The order in which the objects are returned by the create() method needs to be reflected in the order they are passed to the constructor.

So let’s see our revised DemoController:

<?php

/**
 * @file
 * Contains \Drupal\demo\Controller\DemoController.
 */

namespace Drupal\demo\Controller;

use Drupal\Core\Controller\ControllerBase;
use Symfony\Component\DependencyInjection\ContainerInterface;

/**
 * DemoController.
 */
class DemoController extends ControllerBase {
  
  protected $demoService;
  
  /**
   * Class constructor.
   */
  public function __construct($demoService) {
    $this->demoService = $demoService;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container) {
    return new static(
      $container->get('demo.demo_service')
    );
  }
  
  /**
   * Generates an example page.
   */
  public function demo() {
    return array(
      '#markup' => t('Hello @value!', array('@value' => $this->demoService->getDemoValue())),
    );
  }
}

As you can see, all the steps are there. The create() method creates a new instance of our controller class passing to it our service retrieved from the container. And in the end, an instance of the DemoService class gets stored in the $demoService property, and we can use it to call its getDemoValue() method. And this value is then used in the Hello message. Clear your cache and give it a try. Go to the demo/ path and you should see Hello Upchuk! printed on the page.

I’m sure you can see the power of the service container as we can now write decoupled functionality and pass it where it’s needed. I did not show you how, but you can also declare dependencies when you register services. This means that when Drupal instantiates a service object, it will do so for all its dependencies as well, and pass them to its constructor. You can read more about how to do that on this documentation page.

Conclusion

In this article we’ve looked at a lot of cool stuff. We’ve seen how the configuration system manages simple configuration and what we have available form-wise for this. I do encourage you to explore how the ConfigFormBase is implemented and what you have available if you extend it. Additionally, you should play around in the UI with importing/exporting configuration between sites. This will be a great improvement for the deployment process from now on.

Then, we looked at services, what they are and how they work. A great way of maintaining reusable and decoupled pieces of functionality accessible from anywhere. And I do hope the concept of dependency injection is no longer so scary (if it was for you). It is basically the equivalent of passing parameters to procedural functions, but done using constructor methods (or setters), under the hood, by Symfony and its great service container.

Jun 16 2014
Jun 16

How to Build a Drupal 8 Module

In the first installment of this article series on Drupal 8 module development we started with the basics. We’ve seen what files were needed to let Drupal know about our module, how the routing process works and how to create menu links programatically as configuration.

In this tutorial we are going to go a bit further with our sandbox module found in this repository and look at two new important pieces of functionality: blocks and forms. To this end, we will create a custom block that returns some configurable text. After that, we will create a simple form used to print out user submitted values to the screen.

Drupal 8 blocks

A cool new change to the block API in D8 has been a switch to making blocks more prominent, by making them plugins (a brand new concept). What this means is that they are reusable pieces of functionality (under the hood) as you can now create a block in the UI and reuse it across the site – you are no longer limited to using a block only one time.

Let’s go ahead and create a simple block type that prints to the screen Hello World! by default. All we need to work with is one class file located in the src/Plugin/Block folder of our module’s root directory. Let’s call our new block type DemoBlock, and naturally it needs to reside in a file called DemoBlock.php. Inside this file, we can start with the following:

<?php

namespace Drupal\demo\Plugin\Block;

use Drupal\block\BlockBase;
use Drupal\Core\Session\AccountInterface;

/**
 * Provides a 'Demo' block.
 *
 * @Block(
 *   id = "demo_block",
 *   admin_label = @Translation("Demo block"),
 * )
 */

class DemoBlock extends BlockBase {
  
  /**
   * {@inheritdoc}
   */
  public function build() {    
    return array(
      '#markup' => $this->t('Hello World!'),
    );
  }
  
  /**
   * {@inheritdoc}
   */
  public function access(AccountInterface $account) {
    return $account->hasPermission('access content');
  }  
  
}

Like with all other class files we start by namespacing our class. Then we use the BlockBase class so that we can extend it, as well as the AccountInterface class so that we can get access to the currently logged in user. Then follows something you definitely have not seen in Drupal 7: annotations.

Annotations are a PHP discovery tool located in the comment block of the same file as the class definition. Using these annotations we let Drupal know that we want to register a new block type (@Block) with the id of demo_block and the admin_label of Demo block (passed through the translation system).

Next, we extend the BlockBase class into our own DemoBlock, inside of which we implement two methods (the most common ones you’ll implement). The build() method is the most important as it returns a renderable array the block will print out. The access() method controls access rights for viewing this block. The parameter passed to it is an instance of the AccountInterface class which will be in this case the current user.

Another interesting thing to note is that we are no longer using the t() function globally for translation but we reference the t() method implemented in the class parent.

And that’s it, you can clear the caches and go to the Block layout configuration page. The cool thing is that you have the block types on the right (that you can filter through) and you can place one or more blocks of those types to various regions on the site.

Drupal 8 block configuration

Now that we’ve seen how to create a new block type to use from the UI, let’s tap further into the API and add a configuration form for it. We will make it so that you can edit the block, specify a name in a textfield and then the block will say hello to that name rather than the world.

First, we’ll need to define the form that contains our textfield. So inside our DemoBlock class we can add a new method called blockForm():

/**
 * {@inheritdoc}
 */
public function blockForm($form, &$form_state) {
  
  $form = parent::blockForm($form, $form_state);
  
  $config = $this->getConfiguration();

  $form['demo_block_settings'] = array(
    '#type' => 'textfield',
    '#title' => $this->t('Who'),
    '#description' => $this->t('Who do you want to say hello to?'),
    '#default_value' => isset($config['demo_block_settings']) ? $config['demo_block_settings'] : '',
  );
  
  return $form;
}

This form API implementation should look very familiar from Drupal 7. There are, however, some new things going on here. First, we retrieve the $form array from the parent class (so we are building on the existing form by adding our own field). Standard OOP stuff. Then, we retrieve and store the configuration for this block. The BlockBase class defines the getConfiguration() method that does this for us. And we place the demo_block_settings value as the #default_value in case it has been set already.

Next, it’s time for the submit handler of this form that will process the value of our field and store it in the block’s configuration:

/**
* {@inheritdoc}
*/
public function blockSubmit($form, &$form_state) {
 
 $this->setConfigurationValue('demo_block_settings', $form_state['values']['demo_block_settings']);
 
} 

This method also goes inside the DemoBlock class and all it does is save the value of the demo_block_settings field as a new item in the block’s configuration (keyed by the same name for consistency).

Lastly, we need to adapt our build() method to include the name to say hello to:

 /**
 * {@inheritdoc}
 */
public function build() {
  
  $config = $this->getConfiguration();
  
  if (isset($config['demo_block_settings']) && !empty($config['demo_block_settings'])) {
    $name = $config['demo_block_settings'];
  }
  else {
    $name = $this->t('to no one');
  }
  
  return array(
    '#markup' => $this->t('Hello @name!', array('@name' => $name)),
  );  
}

By now, this should look fairly easy. We are retrieving the block’s configuration and if the value of our field is set, we use it for the printed statement. If not, use use a generic one. You can clear the cache and test it out by editing the block you assigned to a region and add a name to say hello to. One thing to keep in mind is that you are still responsible for sanitizing user input upon printing to the screen. I have not included these steps for brevity.

Drupal 8 forms

The last thing we are going to explore in this tutorial is how to create a simple form. Due to space limitations, I will not cover the configuration management aspect of it (storing configuration values submitted through forms). Rather, I will illustrate a simple form definition, the values submitted being simply printed on the screen to show that it works.

In Drupal 8, form definition functions are all grouped together inside a class. So let’s define our simple DemoForm class inside src/Form/DemoForm.php:

<?php

/**
 * @file
 * Contains \Drupal\demo\Form\DemoForm.
 */

namespace Drupal\demo\Form;

use Drupal\Core\Form\FormBase;

class DemoForm extends FormBase {
  
  /**
   * {@inheritdoc}.
   */
  public function getFormId() {
    return 'demo_form';
  }
  
  /**
   * {@inheritdoc}.
   */
  public function buildForm(array $form, array &$form_state) {
    
    $form['email'] = array(
      '#type' => 'email',
      '#title' => $this->t('Your .com email address.')
    );
    $form['show'] = array(
      '#type' => 'submit',
      '#value' => $this->t('Submit'),
    );
    
    return $form;
  }
  
  /**
   * {@inheritdoc}
   */
  public function validateForm(array &$form, array &$form_state) {
    
    if (strpos($form_state['values']['email'], '.com') === FALSE ) {
      $this->setFormError('email', $form_state, $this->t('This is not a .com email address.'));
    } 
  }
  
  /**
   * {@inheritdoc}
   */
  public function submitForm(array &$form, array &$form_state) {
    
    drupal_set_message($this->t('Your email address is @email', array('@email' => $form_state['values']['email'])));
  }
  
}

Apart from the OOP side of it, everything should look very familiar to Drupal 7. The Form API has remained pretty much unchanged (except for the addition of some new form elements and this class encapsulation). So what happens above?

First, we namespace the class and use the core FormBase class so we can extend it with our own DemoForm class. Then we implement 4 methods, 3 of which should look very familiar. The getFormId() method is new and mandatory, used simply to return the machine name of the form. The buildForm() method is again mandatory and it builds up the form. How? Just like you are used to from Drupal 7. The validateForm() method is optional and its purpose should also be quite clear from D7. And finally, the submitForm() method does the submission handling. Very logical and organised.

So what are we trying to achieve with this form? We have an email field (a new form element in Drupal 8) we want users to fill out. By default, Drupal checks whether the value input is in fact an email address. But in our validation function we make sure it is a .com email address and if not, we set a form error on the field. Lastly, the submit handler just prints a message on the page.

One last thing we need to do in order to use this form is provide a route for it. So edit the demo.routing.yml file and add the following:

demo.form:
  path: '/demo/form'
  defaults:
    _form: '\Drupal\demo\Form\DemoForm'
    _title: 'Demo Form'
  requirements:
    _permission: 'access content'

This should look familiar from the previous article in which we routed a simple page. The only big difference is that instead of _content under defaults, we use _form to specify that the target is a form class. And the value is therefore the class name we just created.

Clear the caches and navigate to demo/form to see the form and test it out.

If you are familiar with drupal_get_form() and are wondering how to load a form like we used to in Drupal 7, the answer is in the global Drupal class. Thus to retrieve a form, you can use its formBuilder() method and do something like this:

$form = \Drupal::formBuilder()->getForm('Drupal\demo\Form\DemoForm');

Then you can return $form which will be the renderable array of the form.

Conclusion

In this article we’ve continued our exploration of Drupal 8 module development with two new topics: blocks and forms. We’ve seen how to create our own block type we can use to create blocks in the UI. We’ve also learned how to add a custom configuration to it and store the values for later use. On the topic of forms, we’ve seen a simple implementation of the FormBase class that we used to print out to the screen the value submitted by the user.

In the next tutorial we will take a quick look at configuration forms. We will save the values submitted by the user using the Drupal 8 configuration system. Additionally, we will look at the service container and dependency injection and how those work in Drupal 8. See you then.

Jun 13 2014
Jun 13

How to Build a Drupal 8 Module

Drupal 8 brings about a lot of changes that seek to enroll it in the same club other modern PHP frameworks belong to. This means the old PHP 4 style procedural programming is heavily replaced with an object oriented architecture. To achieve this, under the initiative of Proudly Found Elsewhere, Drupal 8 includes code not developed specifically for Drupal.

One of the most important additions to Drupal are Symfony components, with 2 major implications for Drupal developers. First, it has the potential to greatly increase the number of devs that will now want to develop for Drupal. And second, it gives quite a scare to some of the current Drupal 7 developers who do not have much experience with modern PHP practices. But that’s ok, we all learn, and lessons taken from frameworks like Symfony (and hopefully Drupal 8), will be easily extensible and applicable to other PHP frameworks out there.

In the meantime, Drupal 8 is in a late stage of its release cycle, the current version at the time of writing being alpha11. We will use this version to show some of the basic changes to module development Drupal 7 devs will first encounter and should get familiar with. I set up a Git repo where you can find the code I write in this series so you can follow along like that if you want.

How do I create a module?

The first thing we are going to look at is defining the necessary files and folder structure to tell Drupal 8 about our new module. In Drupal 7 we had to create at least 2 files (.info and .module), but in Drupal 8, the YAML version of the former is enough. And yes, .info files are now replaced with .info.yml files and contain similar data but structured differently.

Another major change is that custom and contrib module folders now go straight into the root modules/ folder. This is because all of the core code has been moved into a separate core/ folder of its own. Of course, within the modules/ directory, you are encouraged to separate modules between custom and contrib like in Drupal 7.

Let’s go ahead and create a module called demo (very original) and place it in the modules/custom/ directory. And as I mentioned, inside of this newly created demo/ folder, all we need to begin with is a demo.info.yml file with the following required content:

name: Drupal 8 Demo module
description: 'Demo module for Drupal 8 alpha11'
type: module
core: 8.x

Three out of four you should be familiar with (name, description and core). The type is now also a requirement as you can have yml files for themes as well. Another important thing to keep in mind is that white spaces in yml files mean something and proper indentation is used to organize data in array-like structures.

You can check out this documentation page for other key|value pairs that can go into a module .info.yml file and the change notice that announced the switch to this format.

And that’s it, one file. You can now navigate to the Extend page, find the Demo module and enable it.

As I mentioned, we are no longer required to create a .module file before we can enable the module. And architecturally speaking, the .module files will be significantly reduced in size due to most of the business logic moving to service classes, controllers and plugins, but we’ll see some of that later.

What is ‘routing’ and what happened to hook_menu() and its callbacks?

In Drupal 7, hook_menu() was probably the most implemented hook because it was used to define paths to Drupal and connect these paths with callback functions. It was also responsible for creating menu links and a bunch of other stuff.

In Drupal 8 we won’t need hook_menu() anymore as we make heavy use of the Symfony2 components to handle the routing. This involves defining the routes as configuration and handling the callback in a controller (the method of a Controller class). Let’s see how that works by creating a simple page that outputs the classic Hello world!.

First, we need to create a routing file for our module called demo.routing.yml. This file goes in the module root folder (next to demo.info.yml). Inside this file, we can have the following (simple) route definition:

demo.demo:
  path: '/demo'
  defaults:
    _content: '\Drupal\demo\Controller\DemoController::demo'
    _title: 'Demo'
  requirements:
    _permission: 'access content'

The first line marks the beginning of a new route called demo for the module demo (the first is the module name and the second the route name). Under path, we specify the path we want this route to register. Under defaults, we have two things: the default page title (_title) and the _content which references a method on the DemoController class. Under requirements, we specify the permission the accessing user needs to have to be able to view the page. You should consult this documentation page for more options you can have for this routing file.

Now, let’s create our first controller called DemoController that will have a method named demo() getting called when a user requests this page.

Inside the module directory, create a folder called src/ and one called Controller/ inside of it. This will be the place to store the controller classes. Go ahead and create the first one: DemoController.php.

The placement of the Controllers and, as we will see, other classes, into the src/ folder is part of the adoption of the PSR-4 standard. Initially, there was a bigger folder structure we had to create (PSR-0 standard) but now there is a transition phase in which both will work. So if you still see code placed in a folder called lib/, that’s PSR-0.

Inside of our DemoController.php file, we can now declare our class:

<?php
/**
 * @file
 * Contains \Drupal\demo\Controller\DemoController.
 */

namespace Drupal\demo\Controller;

/**
 * DemoController.
 */
class DemoController {
  /**
   * Generates an example page.
   */
  public function demo() {
    return array(
      '#markup' => t('Hello World!'),
    );
  }      
}

This is the simplest and minimum we need to do in order to get something to display on the page. At the top, we specify the class namespace and below we declare the class.

Inside the DemoController class, we only have the demo() method that returns a Drupal 7-like renderable array. Nothing big. All we have to do now is clear the caches and navigate to http://example.com/demo and we should see a Drupal page with Hello World printed on it.

In Drupal 7, when we implement hook_menu(), we can also add the registered paths to menus in order to have menu links showing up on the site. This is again no longer handled with this hook but we use a yml file to declare the menu links as configuration.

Let’s see how we can create a menu link that shows up under the Structure menu of the administration. First, we need to create a file called demo.menu_links.yml in the root of our module. Inside this yml file we will define menu links and their position in existing menus on the site. To achieve what we set out to do, we need the following:

demo.demo:
  title: Demo Link
  description: 'This is a demo link'
  parent: system.admin_structure
  route_name: demo.demo

Again we have a yml structure based on indentation in which we first define the machine name of the menu link (demo) for the module demo (like we did with the routing). Next, we have the link title and description followed by the parent of this link (where it should be placed) and what route it should use.

The value of parent is the parent menu link (appended by its module) and to find it you need to do a bit of digging in *.menu_links.yml files. I know that the Structure link is defined in the core System module so by looking into the system.menu_links.yml file I could determine the name of this link.

The route_name is the machine name of the route we want to use for this link. We defined ours earlier. And with this in place, you can clear the cache and navigate to http://example.com/admin/structure where you should now see a brand new menu link with the right title and description and that links to the demo/ path. Not bad.

Conclusion

In this article we began exploring module development in Drupal 8. At this stage (alpha11 release), it is time to start learning how to work with the new APIs and port contrib modules. To this end, I am putting in writing my exploration of this new and exiting framework that will be Drupal 8 so that we can all learn the changes and hit the ground running when release day comes.

For starters, we looked at some basics: how you start a Drupal 8 module (files, folder structure etc), all compared with Drupal 7. We’ve also seen how to define routes and a Controller class with a method to be called by this route. And finally, we’ve seen how to create a menu link that uses the route we defined.

In the next tutorial, we will continue building this module and look at some other cool new things Drupal 8 works with. We will see how we can create blocks and how to work with forms and the configuration system. See you then.

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