Purges the field data for a single field on a single pseudo-entity.
This is basically the same as field_attach_delete() except it only applies to a single field. The entity itself is not being deleted, and it is quite possible that other field data will remain attached to it.
$entity_type: The type of $entity; e.g. 'node' or 'user'.
$entity: The pseudo-entity whose field data is being purged.
$field: The (possibly deleted) field whose data is being purged.
$instance: The deleted field instance whose data is being purged.
function field_purge_data($entity_type, $entity, $field, $instance) {
// Each field type's hook_field_delete() only expects to operate on a single
// field at a time, so we can use it as-is for purging.
$options = array(
'field_id' => $instance['field_id'],
'deleted' => TRUE,
);
_field_invoke('delete', $entity_type, $entity, $dummy, $dummy, $options);
// Tell the field storage system to purge the data.
module_invoke($field['storage']['module'], 'field_storage_purge', $entity_type, $entity, $field, $instance);
// Let other modules act on purging the data.
foreach (module_implements('field_attach_purge') as $module) {
$function = $module . '_field_attach_purge';
$function($entity_type, $entity, $field, $instance);
}
}