Changing the view mode of EntityReferenceFieldItems programmatically

Question

I have a paragraph (I'm using the Paragraphs module) that contains an entity reference field that contains references to other pages.

The display settings are set to use a particular view mode, e.g. teaser. This renders an teaser image, title and link to the page.

I would like the editor to be able to set the view mode on a per-paragraph basis. I have created a "view mode" field in the paragraph with two options: teaser, and teaser-text-only.

How can I use the view mode set in the "parent" entity (the paragraph) to add a template suggestion when rendering the "child" entities (the pages)?

Answer 1

At this point it should be no problem to change the view mode in the render element of the referenced node. The node has yet to be built and will, hopefully, use the modified view mode.

You can try something like this in a paragraph preprocess hook:

function mytheme_preprocess_paragraph(&$variables) {

  if ($variables['paragraph']->hasField('field_view_mode')) {
    $view_mode = $variables['paragraph']->field_view_mode->value;
    if (isset($variables['content']['field_ref_node']['0']['#view_mode'])) {
      $variables['content']['field_ref_node']['0']['#view_mode'] = $view_mode;
      unset($variables['content']['field_ref_node']['0']['#cache']['keys']);
    }
  }

}

Edit:

To prevent that the node gets cached on it's own in the wrong view mode remove the cache key.

Answer 2

There is a module view_mode_selector that should allow for this now. There is currently a dev releases for D8.

A small module which allows you to change the view mode of an entity.

This module provides a new field type "View mode selector", so just go to "Manage fields" and create a field of that type and choose between a "select list" and a "radio buttons" widget. When you choose "radio buttons" it is possible to upload an icon which will be displayed instead of the view mode name.

In order to display your referenced entities with the new "View mode selector" view mode don't forget to change the view mode on "Manage display" which is used for displaying them.

If Display Suite is enabled, it can also display a live preview of the configured view mode layout. Here is an example:

Answer 3

Bit late to the party here but here's how I just did it using Drupal 7.

I have a paragraph type called Related Content (related_content) with 2 fields: An entity reference field and a Select (text) field called field_related_content_view_mode

I have set the default display mode of the referenced entities / field_related content in the field display of the related content paragraph and use hook_field_display_alter() to alter the display mode to the one set by field_related_content_view_mode:

/**
 * Implements hook_field_display_alter().
 */
function mymodule_field_display_alter(&$display, $context) {
  if ($context['entity_type'] == 'paragraphs_item') {
    if ($context['field']['field_name'] == 'field_related_content') {
      $entity = $context['entity'];
      if (isset($entity->field_related_content_view_mode) && !empty($entity->field_related_content_view_mode)) {
        $view_mode = $entity->field_related_content_view_mode[LANGUAGE_NONE][0]['value'];
        $display['settings']['view_mode'] = $view_mode;
      }
    }
  }
}