How to correctly access entity elements in a twig template

Question

I have an array of entities that i would like to render in a list.

$ids = \Drupal::entityQuery('chemical')
  ->condition('tid', $tid)
  ->execute();
$controller = \Drupal::entityManager()->getStorage('chemical');
$entities = $controller->loadMultiple($ids);

$chemicals = [];
foreach ($entities as $entity){
  $chemicals[] = ['id' => $entity->id(), 'label' => $entity->label()];
}

$output[] = [
  '#theme' => 'chemical_taxonomy',
  '#chemicals' => $chemicals,
];
return $output;

The twig template then creates the unordered list of URLs using the array of {{ chemicals.label }} and {{ chemicals.id }}. However, I should be able to just pass $entities to the template instead of extracting the id and label and building a new array, shouldn't I?

If I replace '#chemicals' => $chemicals with '#chemicals' => $entities I receive an error:

Uncaught PHP Exception Exception: "Object of type Drupal\\Core\\Field\\FieldItemList cannot be printed." at /var/www/Drupal_Sites/console/core/lib/Drupal/Core/Template/TwigExtension.php line 443,   

Answer 1

As the exception explains, you tried to print an object that is not renderable and cannot be converted to a string. In this case it was Drupal\Core\Field\FieldItemList which is the object returned by drupal entities when you ask for a field ({{ entity.id }} / {{ entity.label }}).

To get the actual value you need to call to methods of your entity (the actual value of the fields is protected from outside access).

The long way:

{{ entity.get('id').get(0).get('value').getValue() }}

The above is the actual path you need to take to get from the entity object to the value of the id field.

However drupal supplies shortcuts through what is known as magic properties. The short way

{{ entity.id.value }}

Answer 2

To get the full objects in your twig file, you could have done this:

$ids = \Drupal::entityQuery('chemical')
  ->condition('tid', $tid)
  ->execute();
$controller = \Drupal::entityManager()->getStorage('chemical');
$entities = $controller->loadMultiple($ids);

$output[] = [
  '#theme' => 'chemical_taxonomy',
  '#chemicals' => $entities,
];
return $output;

Then, in your twig file just do:

<ul>
{% for chemical in chemicals %}
  <li data-id="{{ chemical.id() }}">{{ chemical.label() }}</li>
{% endfor %}
</ul>

Answer 3

You have to implement function template_preprocess_chemical_taxonomy(&$variables) where you prepare you variables for your template.

As an example have a look in core regarding function template_preprocess_item_list(&$variables) for item-list.html.twig.

Answer 4

You have to render the entity before passing it to twig.

$render_controller = \Drupal::entityManager()->getViewBuilder('chemical');

foreach ($entities as $entity){
  $chemicals[] = $render_controller->view($entity);
}

Of course, this means creating a custom viewbuilder for your entity, if you haven't already, which may be more work, but would a nicer solution than creating a custom array each time you want to render your entity.

You could copy another view builder, such as core/modules/node/src/NodeViewBuilder.php

move it into your project and alter it to work with your custom entity.