Entity Data

Entity data provides a simple API to add data to any entity. It works similar to core's variable_set/get/del system. Except the data is associated with a entity and only loaded when that entity is loaded.

The primary usage involves the getter/setter methods:
entity_data_set($entity_type, $entity_id, $name, $value, $revision_id = 0, $language = LANGUAGE_NONE);

entity_data_get($entity_type, $entity_id, $name, $default = NULL, $revision_id = 0, $language = LANGUAGE_NONE);

entity_data_del($entity_type, $entity_id, $name, $revision_id = 0, $language = LANGUAGE_NONE);

In addition to using the getter/setter methods, entity_data is automatically attached on entity_load and saved on entity_insert/entity_update. The data can be accessed using following the format:
$entity->entity_data[$name]

This also means that entity data will export and import with the entity.