Pass node field value to page.html.twig

Question

I'm new to Drupal. I've just started a custom theme in Drupal 8 and created a new field under Content Type. This field value is a custom class for each page. From the documentation I should be able to display the field contents of "field_body_class" with the following, neither of which display.

{{content.field_body_class}}

{{page.content.field_body_class}}

I've checked to make sure the field was not hidden, which it was not.

Answer 1

You are probably a bit confused.

Variables are only available in specific templates. So the value of a field which is attached to an entity (like a content type) is only available in the template for that entity.

To make the body class field value available in a different template you need to

• make a preprocess function for the template.
• fetch the entity that has the field
• expose it to the template.

For you it could look something like this.

function theme_name_preprocess_page(&$variables) {
   // Define {{ body_class }}  in the template.
  if (!empty($variables['node']) && !empty($variables['node']->field_body_class)) {
    $variables['body_class'] = $variables['node']->field_body_class->value;
  }
}

Answer 2

The page.html.twig template doesn't get any content variable. It gets a page.content variable, but that is the rendered content of the content region, which means you won't get page.content.field_body_class.

To get the field value, you need to implement a preprocess function for the node template and set a new variable initialized to the field value.

function mytheme_preprocess_node(&$variables) {
  if (!empty($variables['node']->field_body_class)) {
    $variables['body_class'] = $variables['node']->get('field_body_class')->value;
  }
}