Call preprocess_node (or get variables) from Twig template?

Question

I have the following content types (for a simple LMS) defined:

• Lessons, for which there are rather complex rules for handling view access.
• Courses, which contain entity references to one or more Lessons.

Now, in the Twig template for rendering a Course node, I am trying to create a "table of contents" (a list of Lessons), using the following snippet:

<nav id='toc_lessons' class="list-group">
  {% for key, lesson in content.field_lessons %}
    {% if lesson['#node'].title.value|render|striptags|trim %}

        <a class="list-group-item list-group-item-action
           href="{{ url('<current>') }}/?lesson={{ lesson['#node'].nid.value }}">
          {{ lesson['#node'].title.value }}
          {{ (*****) ? '<span class="label">LOCKED</span>' }}
        </a>

    {% endif %}
  {% endfor %}
</nav>

This works well. However, the problem with this code is the line that I marked with (*****): I would like to do a simple access check, i.e. I would like to check, if the user is allowed to view the Lesson. If not, the label "LOCKED" should be added.

In my implementation of function THEME_preprocess_node I have already defined such a check that is called whenever a Lesson is rendered:

function THEME_preprocess_node(&$variables) {
  ...
  $node = $variables['elements']['#node'];
  $variables['viewaccess'] = $node->access('view');
  ...
}

But can I call the preprocessing function for a Lesson from within the Course template to receive the variable viewaccess?

Another idea would be to modify the above snippet as follows:

<nav id='toc_lessons' class="list-group">
  {% for key, lesson in content.field_lessons %}
    {% if lesson['#node'].title.value|render|striptags|trim %}

        {{ bamboo_render_entity('node', lesson['#node'].nid.value, 'toc_entry') }}

    {% endif %}
  {% endfor %}
</nav>

so, I am now rendering the Lesson using Bamboo Twig and the output <a>...</a> is fully handled by the Lesson template, which works fine. The problem now is that a Lesson that the user does not have view access for, is not rendered at all.

Now, I'm stuck. Can anybody offer any ideas?

Any help would be much appreciated.

Answer 1

You're pretty close. I think there are a couple of approaches to this. This is what I would do

preprocess the lessons entity reference field for the courses bundle, iterate through the values, check the access, set a variable with the access value for each item. Then in field--field-lessons.twig.html, render the field if the access value is true.

<?php
//the name of your lessons entity reference field on courses
function THEME_preprocess_field__field_lessons(&$variables) {

  if($variables['element']['#bundle'] == 'courses') {
    $account = \Drupal::currentUser();
    $ent_refs = $variables['element']['#items']->referencedEntities();

    foreach ($ent_refs as $key => $ent_ref) {
      $check = $ent_ref->access('view', $account);
      $variables['items'][$key]['my_access'] = FALSE;

      if ($check) {
        $variables['items'][$key]['my_access'] = TRUE;
      }
    }

  }
}

then in field--field-lessons.twig.html

...
{% for item in items %}
    {% if item.my_access == TRUE %}
      I'm Unlocked: {{ item.content }}
    {% else %}
      I'm locked :(
    {% endif %}
  {% endfor %}
...