Decorating an Entity Metadata Wrapper to add and refactor methods

Following yesterday's Entity Metadata Wrapper blog post and as I continued to work on this task, I noticed some duplication and found that I was repeating several of the same chaining steps in different methods in the same file. For example:

public function getFirstName(): string {
return $this
->get('profile_user_basic') // Get the pupil's profile.
->get('field_first_name')
->value();
}

private function getTeacherFirstName(): string {
$this
->get('profile_student') // Get the pupil's profile.
->get('field_class') // Get the pupil's class.
->get('field_teacher') // Get the class' teacher.
->get('profile_user_basic') // Get the teacher's profile.
->get('field_first_name')
->value();
}

In both cases, the last three lines are the same, where the same profile type is loaded, and the value is loaded from a field.

I wanted to find a way to remove this duplication whilst also making the code more readable. Ideally, this would mean adding a method like getFirstNameFromBasicProfile() that would group the last three steps.

Extending the EntityDrupalWrapper

I've done this before, where I've created a custom wrapper class with its own methods and extends EntityDrupalWrapper. This is how that might look:

final class PupilWrapper extends \EntityDrupalWrapper {

public function __construct(\stdClass $data, $info = []) {
parent::__construct('user', $data, $info);
}

public function getFirstName(): string {
return $this->getFirstNameFromBasicProfile();
}

public function getTeacherFirstName(): string {
return $this
->get('profile_student')
->get('field_class')
->get('field_teacher')
->getFirstNameFromBasicProfile();
}

private function getFirstNameFromBasicProfile(): string {
return $this
->get('profile_user_basic')
->get('field_first_name')
->value();
}

}

Whilst this has worked in previous situations, this time I had this error:

Error: Call to undefined method EntityDrupalWrapper::getFirstNameFromBasicProfile() in Drupal\my_module\EntityWrapper\PupilWrapper->getTeacherFirstName

This is because the get() method is returning an instance of EntityStructureWrapper (another class that extends EntityDrupalWrapper) which means that getFirstNameFromBasicProfile() is not accessible though it's in the same file.

I tried overriding the get() method but wasn't able to get this to work.

Decorating the EntityDrupalWrapper

Another option that I tried was to follow the Decorator design pattern, and add a new class that takes an EntityDrupalWrapper as an argument as uses it internally but doesn't extend it. Here's an example:

final class PupilWrapper {

private $accountWrapper;

public function __construct(\EntityMetadataWrapper $accountWrapper) {
$this->accountWrapper = $accountWrapper;
}

public function getFirstName(): string {
return $this->getFirstNameFromBasicProfile();
}

public function getTeacherFirstName(): string {
return $this
->get('profile_student')
->get('field_class')
->get('field_teacher')
->getFirstNameFromBasicProfile();
}

private function getFirstNameFromBasicProfile(): string {
return $this
->get('profile_user_basic')
->get('field_first_name')
->value();
}

}

In this case, the constructor argument is an instance of EntityMetadataWrapper so that it could be either an EntityDrupalWrapper or EntityStructureWrapper.

Re-adding required wrapper methods

As the get() method is missing, this would cause an error:

Error: Call to undefined method Drupal\my_module\EntityWrapper\PupilWrapper::get() in Drupal\my_module\EntityWrapper\PupilWrapper->getFirstName()

However, we can re-add it, have it get the value from accountWrapper and return another instance of PupilWrapper so that getFirstNameFromBasicProfile() will be available.

public function get(string $property): self {
return new self($this->accountWrapper->get($property));
}

The value() method is also required, but this can delegate to the decorated wrapper:

Error: Call to undefined method Drupal\my_module\EntityWrapper\PupilWrapper::value() in Drupal\my_module\EntityWrapper\PupilWrapper->getFirstName()

public function value(): string {
return $this->accountWrapper->value();
}

Conclusion

This was the first time that I tried extending Drupal 7's entity metadata wrappers in this way, but it worked well, removes the duplication and cleans up the code further.