Loop through child elements in Twig like Element::children()

Question

When dealing with a renderable array in PHP, I can use Element::children() to access the elements that are not # properties but subordinated renderable elements (form items inside a fieldset, items inside a field widget, etc). For instance, this snippet from file.module:

<?php
if ($element['#multiple']) {
  foreach (Element::children($element) as $name) {
    // ...
  }
}
?>

How can I do the same in a Twig template? If I do {% for child in element %}, it will include also #type, #cache etc.

Answer 1

{% for key, child in element if key|first != '#' %}
  <div>{{ child }}</div>
{% endfor %}

Answer 2

Use the Twig Tweak module, which, among other wonderful features, has a "children" filter:

{% for item in content.field_name | children(true) %}
  {# loop.length, loop.revindex, loop.revindex0, and loop.last are now available #}
{% endfor %}

Answer 3

I have created a Twig filter that returns back with the children as an ArrayIterator.

mymodule/mymodule.services.yml

services:
  mymodule.twig_extension:
    arguments: ['@renderer']
    class: Drupal\mymodule\TwigExtension\Children
    tags:
      - { name: twig.extension }

mymodule/src/TwigExtension/Children.php

<?php

namespace Drupal\mymodule\TwigExtension;


class Children extends \Twig_Extension
{

  /**
   * Generates a list of all Twig filters that this extension defines.
   */
  public function getFilters()
  {
    return [
      new \Twig_SimpleFilter('children', array($this, 'children')),
    ];
  }


  /**
   * Gets a unique identifier for this Twig extension.
   */
  public function getName()
  {
    return 'mymodule.twig_extension';
  }


  /**
   * Get the children of a field (FieldItemList)
   */
  public static function Children($variable)
  {
    if (!empty($variable['#items'])
      && $variable['#items']->count() > 0
    ) {
      return $variable['#items']->getIterator();
    }

    return null;
  }

}

in the Twig template:

{% for headline in entity.field_headline|children %}
  {{ headline.get('value').getValue() }}
{% endfor %}

Answer 4

Since Twig 2.10.0 using "if" in a "for" loop is deprecated, and you'll have to use filter.

{% for key, child in element if key|first != '#' %}
  <div>{{ child }}</div>
{% endfor %}

would become

{% for key, child in element|filter((child, key) => key|first != '#') %}
  <div>{{ child }}</div>
{% endfor %}

Answer 5

Here's a modification of https://drupal.stackexchange.com/a/236408/67965 that loops through the render children instead of the field #items.

The twig extension:

/**
 * Generates a list of all Twig filters that this extension defines.
 */
public function getFilters() {
  return [
    new \Twig_SimpleFilter('children', array($this, 'children')),
  ];
}

/**
 * Get the render children of a field
 */
public static function children($variable) {
  return array_filter(
    $variable, 
    function($k) { return (is_numeric($k) || (strpos($k, '#') !== 0)); },
    ARRAY_FILTER_USE_KEY
  );
}

In twig, you can then pass through rendered children directly, which helps in atomic design patterns. Define an entity template, for instance:

{% include '@molecules/grid.html.twig' with { 
   head : content.field_title,
   grid_columns: content.field_collection_items|children
} %}

where grid.html.twig is something like:

{% if head %}
<div class="slab__wrapper">
  {{ head }}
</div>
{% endif %}
<div class="grid">          
  {% for col in grid_columns %}
  <div class="grid__column">
    {{ col }}
  </div>
  {% endfor %}
</div>

This is usually more useful than having to render a field template for {{ content.field_collection_items }} because the layout of the children may be controlled in the context of the parent design element.