Drupal - How to write a property callback for a custom field to use with the Entity module

Kind of :) ... if its just numbers and strings you can cheat a little. I added some basic integer columns to the User table and wanted EntityAPI and views etc to be aware of them and did the following:

/**
 * Implementation of hook_entity_property_info(). This dpeends on the EntityAPI.
 *
 * This defines the properties/attributes/"fields" of our Entity regardless of
 * whether they are drupal Fields or custom data (in the base table).
 */
function dew_nagging_entity_property_info_alter(&$info) {
  $properties = &$info['user']['properties'];
  $properties['dew_survey_count_to_complete'] = array(
    'label' => t('Number of Surveys to Complete'),
    'type' => 'integer',
    'description' => 'When a student logs in the system derives how many surveys they must complete. We store this value to make sending the nag email business logic easier.',
    'schema field' => 'dew_survey_count_to_complete',
    'getter callback' => 'entity_property_verbatim_get',
    'setter callback' => 'entity_property_verbatim_set',
  );
  $properties['dew_survey_completed_count'] = array(
    'label' => t('Number of Completed Surveys to Date'),
    'type' => 'integer',
    'description' => 'This is a count of the completed surveys completed by a student in real-time. We store this value to make sending the nag email business logic easier.',
    'schema field' => 'dew_survey_completed_count',
    'getter callback' => 'entity_property_verbatim_get',
    'setter callback' => 'entity_property_verbatim_set',
  );
  $properties['dew_surveys_all_completed'] = array(
    'label' => t('Has the student completed all their Surveys?'),
    'type' => 'integer',
    'description' => 'This is a boolean indictator (0,1) of whether or not a student has completed their surveys. We store this value to make sending the nag email business logic easier.',
    'schema field' => 'dew_surveys_all_completed',
    'getter callback' => 'entity_property_verbatim_get',
    'setter callback' => 'entity_property_verbatim_set',
  );
  return $info;
}

entity_property_verbatim_set and *_get just pull the field from the database if $info['schema field'] is defined.

I also had to make the DB changes in my .install file with db_add_field() for each database column. I also had to notify EntityAPI of my schema changes to the user table via hook_schema_alter(). All these DB schema fields and EntityAPI meta data field defintions must correlate properly.

---

if its more complicated, you do something like found in Ubercart products, you're just returning the item from the given Node and Field.

See http://api.ubercart.me/api/drupal/ubercart%21uc_order%21uc_order.module/function/uc_order_uc_order_get_properties/7.

EDIT

Apparently the entity_metadata_* functions have been deprecated and you should call entity_property_verbatim_get(), or entity_property_verbatim_set().