Attaches a file field to an entity.
$name: The name of the new field (all lowercase), exclude the "field_" prefix.
$entity_type: The entity type this field will be added to.
$bundle: The bundle this field will be added to.
$field_settings: A list of field settings that will be added to the defaults.
$instance_settings: A list of instance settings that will be added to the instance defaults.
$widget_settings: A list of widget settings that will be added to the widget defaults.
function attachFileField($name, $entity_type, $bundle, $instance_settings = array(), $widget_settings = array()) {
$instance = array(
'field_name' => $name,
'label' => $name,
'entity_type' => $entity_type,
'bundle' => $bundle,
'required' => !empty($instance_settings['required']),
'settings' => array(),
);
$instance['settings'] = array_merge($instance['settings'], $instance_settings);
field_create_instance($instance);
entity_get_form_display($entity_type, $bundle, 'default')
->setComponent($name, array(
'type' => 'file_generic',
'settings' => $widget_settings,
))
->save();
}