How do you return an entity property of 'type' => 'struct'

Question

I am using Drupal 7.x and have a created a custom entity. I am using the Entity API module to extend EntityDefaultMetadataController and override public function entityPropertyInfo() to add properties for displaying when my entity is viewed.

More information on hook_property_entity_info:

http://www.drupalcontrib.org/api/drupal/contributions!entity!entity.api.php/function/hook_entity_property_info/7

I understand how to return different types of properties such as 'text', 'int', 'list', 'entity', and so on, using callbacks. However, I have not been able to successfully return a type of 'struct'. My field is always empty when I try to display it.

Example code:

  $info['properties']['my-structure_property'] = array(
  'label' => t('My Structure Property'),  
  'type' => 'struct',
  'getter callback' => ?  // What should this return?
  'property info' => array(
    'sub_field1' => array(
      'type' => 'text', 
      'label' => t('Subfield 1'), 
      'getter callback' => 'entity_metadata_sub_field1_property_get', // Returns a text field
    ), 
    'sub_field2' => array(
      'type' => 'entity', 
      'label' => t('Subfield 1'), 
      'getter callback' => 'entity_metadata_sub_field2_property_get', // Returns an entity
    ), 
  ),
); 

What should I be returning in my callback? I have tried returning an object, an array...?

Answer 1

Based on entity_metadata_node_entity_property_info_alter() and entity_property_text_formatted_info(), I suppose the getter callback should be the most generic callback the entity API offers: entity_property_verbatim_get.

This should allow you to access the properties as: $custom_entity->structure_property->sub_field1