Subscriptions by Reference

This module will allow users to subscribe to new content based on reference fields (see http://drupal.org/node/286789).

Module supports both node references and entity references fields on nodes.

Currently this module can be used by developers by adding a hook to their module, which will define the fields that will be available to users for subscription:

/**
 * Implements hook_subscriptions_reference_info()
 */
function mymodule_subscriptions_reference_info() {
  return array(
    'question_answers' => array(
      'parent' => 'question',
      'child' => 'answer',
      'field' => 'field_answers_question',
      'ref_item' => 'nid', // this will be 'target_id' for entity reference
  ));
}

This hook will allow users to receive notifications about new answers created for questions they are subscribed to.

Requirements
This project extends Subscriptions.

Please check #2035667: Error when creating a child node to a parent which is subscribed to after installation, patch from #1853644: subscriptions_get generates pdo exception is required for this module to work.