Field widget value not able to save via ajax

Question

I am trying to create a custom field type widget with a ajax submit handler to save the value of the field to the database without saving the whole node.

Here is my code hook_field_field_info().

function mymodule_field_info() {
  return array(
   'time_logger_time' => array(
   'label' => t('Time loger'),
   'description' => t('Custom Poutine Field'),
   'default_widget' => 'time_logger_time_widget',
   'default_formatter' => 'time_logger_default_formatter',
   ),
  );
 }

Than this is my hook_field_widget_info()

function mymodule_field_widget_info() {
   return array(
   'time_logger_time_widget' => array(
   'label' => t('Default'),
   'field types' => array('time_logger_time'),
  ),
 );
}

And finally my hook_field_widget_form() looks like

function mymodule_field_widget_form(&$form, &$form_state, $field, $instance, $langcode, $items, $delta, $element) {
    $value = isset($items[$delta]['id']) ? $items[$delta]['id'] : '';
     $element['id'] = array(
       '#type' => 'textfield', 
       '#size' => 6,
       '#default_value' => $value
      );

     $element[submit] = array(
      '#type' => 'button',
      '#value'=>'Save',
      '#name' =>  'submit-'. $delta,
      '#ajax' => array(
        'callback' => 'mymodule_ajax_handler',
        'effect' => 'fade',
       ),
   );
   return $element;
 }

Idea is when I click the save button in my widget form it will call my ajax callback load the node, set the value of my field and save the node as follows-

function mymodule_ajax_handler( $form, &$form_state){
     $node = node_load(22);
     dsm( $node);
     $node_wrapper = entity_metadata_wrapper('node', $node);
     $node_wrapper->field_log->set(1);
     $node->save();
 }

But when I click button I am getting some error saying "Notice: Undefined index: field_log in EntityStructureWrapper->getPropertyInfo() (line 334 of /var/www/html/mysite/sites/all/modules/contrib/entity/includes/entity.wrapper.inc)."

If I change my field in the ajax callback to some other field in my content type its saving fine. Like below-

function mymodule_ajax_handler( $form, &$form_state){
 $node = node_load(22);
 $node_wrapper = entity_metadata_wrapper('node', $node);
 $node_wrapper->some_other_field_from_my_content_type->set(1); //This works fine 
 $node->save();
}

Is there anything wrong in my widget form.

Here is my field scheme if someone want to refer-

function mymodule_field_schema($field) {
$schema = array();
$schema['columns']['id'] = array(
    'type' => 'varchar',
    'length' => 50,
    'not null' => FALSE
);
  return $schema;
}

Answer 1

There might be a few issues, but it hard to tell.

First make sure the field is actually on the node. (Source https://www.drupal.org/documentation/entity-metadata-wrappers):

function _wrapper_debug($w) {
  $values = array();
  foreach ($w->getPropertyInfo() as $key => $val) {
    $values[$key] = $w->$key->value();
  }
  return $values;
}

dpm(_wrapper_debug($some_wrapped_object));

If it is there, perhaps you made the field a multi value field (it can hold more then 1 value), in this case you need to assign it like this:

 $node_wrapper->field_log[]->set(1); // Note the extra []

If this does not solve the problem, have a look at the above metadata wrapper page. It comes with a lot of examples en explanations.

Answer 2

Finally I am able to do this with "property_type" in my hook_field_info(). Posting it here hope someone will get some help someday.

Following is my updated hook_field_info -

function mymodule_field_info() {
  return array(
  'time_logger' => array(
  'label' => t('Time loger'),
  'description' => t('Field that keep track time loged on work items.'),
  'default_widget' => 'time_logger_time_default_wedget',
  'default_formatter' => 'time_logger_default_formatter',
  'property_type' => 'my_property_type',
  'property_callbacks' => array('my_property_info_callback'),
  ),
 );
}

Than my property type callback _

function time_logger_property_info_callback(&$info, $entity_type, $field, $instance, $field_type) {
   $property = &$info[$entity_type]['bundles'][$instance['bundle']] ['properties'][$field['field_name']];
   $property['getter callback'] = 'entity_metadata_field_verbatim_get';
   $property['setter callback'] = 'entity_metadata_field_verbatim_set';
   unset($property['query callback']);
  $property['property info']['lid'] = array(
    'type' => 'text',
    'label' => t('Log id'),
    'setter callback' => 'entity_property_verbatim_set',
  );
  $property['property info']['total_loged_time'] = array(
    'type' => 'text',
    'label' => t('Total logged time.'),
    'setter callback' => 'entity_property_verbatim_set',
   );
}

Than finally my ajax callback is here_

function time_logger_log_time( $form, &$form_state){
   global $user;
   $parents = $form_state['triggering_element']['#array_parents'];
   $values = $form_state['values'];
   $field_name = $parents[0];
   $language_code = $parents[1];
   $delta = $parents[2];
   $nid = $form_state['values']['nid'];
    $node_wrapper->$parents[0]->set(array('field1'=>'something','field2'=>'something'));  
    $node_wrapper->save();
 }

Thanks to @Neograph734 for pointing me to the right direction.