Notifications

There are two ways to send notifications in Elgg:
  • Instant notifications
  • Event-based notifications send using a notifications queue

Instant notifications

The generic method to send a notification to a user is via the function notify_user(). It is normally used when we want to notify only a single user. Notification like this might for example inform that someone has liked or commented the user’s post.

The function usually gets called in an action file.

Example:

In this example a user ($user) is triggering an action to rate a post created by another user ($owner). After saving the rating (ElggAnnotation $rating) to database, we could use the following code to send a notification about the new rating to the owner.

// Subject of the notification
$subject = elgg_echo('ratings:notification:subject', array(), $owner->language);

// Summary of the notification
$summary = elgg_echo('ratings:notification:summary', array($user->name), $owner->language);

// Body of the notification message
$body = elgg_echo('ratings:notification:body', array(
        $user->name,
        $owner->name,
        $rating->getValue() // A value between 1-5
), $owner->language);

$params = array(
        'object' => $rating,
        'action' => 'create',
        'summary' => $summary
);

// Send the notification
notify_user($owner->guid, $user->guid, $subject, $body, $params);

Note

The language used by the recipient isn’t necessarily the same as the language of the person who triggers the notification. Therefore you must always remember to pass the recipient’s language as the third parameter to elgg_echo().

Note

The 'summary' parameter is meant for notification plugins that only want to display a short message instead of both the subject and the body. Therefore the summary should be terse but still contain all necessary information.

Enqueued notifications

On large sites there may be many users who have subscribed to receive notifications about a particular event. Sending notifications immediately when a user triggers such an event might remarkably slow down page loading speed. This is why sending of such notifications shoud be left for Elgg’s notification queue.

New notification events can be registered with the elgg_register_notification_event() function. Notifications about registered events will be sent automatically to all subscribed users.

This is the workflow of the notifications system:

  1. Someone does an action that triggers an event within Elgg
    • The action can be create, update or delete
    • The target of the action can be any instance of the ElggEntity class (e.g. a Blog post)
  2. The notifications system saves this event into a notifications queue in the database
  3. When the pluging hook handler for the one-minute interval gets triggered, the event is taken from the queue and it gets processed
  4. Subscriptions are fetched for the user who triggered the event
    • By default this includes all the users who have enabled any notification method for the user at www.site.com/notifications/personal/<username>
  5. Plugins are allowed to alter the subscriptions using the [get, subscriptions] hook
  6. Plugins are allowed to terminate notifications queue processing with the [send:before, notifications] hook
  7. Plugins are allowed to alter the notification parameters with the [prepare, notification] hook
  8. Plugins are allowed to alter the notification subject/message/summary with the [prepare, notification:<action>:<type>:<subtype>] hook
  9. Plugins are allowed to format notification subject/message/summary for individual delivery methods with [format, notification:<method>] hook
  10. Notifications are sent to each subscriber using the methods they have chosen
    • Plugins can take over or prevent sending of each individual notification with the [send, notification:<method>] hook
  11. The [send:after, notifications] hook is triggered for the event after all notifications have been sent

Example

Tell Elgg to send notifications when a new object of subtype “photo” is created:

/**
 * Initialize the photos plugin
 */
function photos_init() {
        elgg_register_notification_event('object', 'photo', array('create'));
}

Note

In order to send the event-based notifications you must have the one-minute CRON interval configured.

Contents of the notification message can be defined with the 'prepare', 'notification:[action]:[type]:[subtype]' hook.

Example

Tell Elgg to use the function photos_prepare_notification() to format the contents of the notification when a new objects of subtype ‘photo’ is created:

/**
 * Initialize the photos plugin
 */
function photos_init() {
    elgg_register_notification_event('object', 'photo', array('create'));
    elgg_register_plugin_hook_handler('prepare', 'notification:create:object:photo', 'photos_prepare_notification');
}

/**
 * Prepare a notification message about a new photo
 *
 * @param string                          $hook         Hook name
 * @param string                          $type         Hook type
 * @param Elgg_Notifications_Notification $notification The notification to prepare
 * @param array                           $params       Hook parameters
 * @return Elgg_Notifications_Notification
 */
function photos_prepare_notification($hook, $type, $notification, $params) {
    $entity = $params['event']->getObject();
    $owner = $params['event']->getActor();
    $recipient = $params['recipient'];
    $language = $params['language'];
    $method = $params['method'];

    // Title for the notification
    $notification->subject = elgg_echo('photos:notify:subject', array($entity->title), $language);

    // Message body for the notification
    $notification->body = elgg_echo('photos:notify:body', array(
        $owner->name,
        $entity->title,
        $entity->getExcerpt(),
        $entity->getURL()
    ), $language);

    // Short summary about the notification
    $notification->summary = elgg_echo('photos:notify:summary', array($entity->title), $language);

    return $notification;
}

Note

Make sure the notification will be in the correct language by passing the reciepient’s language into the elgg_echo() function.

Registering a new notification method

By default Elgg has two notification methods: email and the bundled site_notifications plugin. You can register a new notification method with the elgg_register_notification_method() function.

Example:

Register a handler that will send the notifications via SMS.

/**
 * Initialize the plugin
 */
function sms_notifications_init () {
        elgg_register_notification_method('sms');
}

After registering the new method, it will appear to the notification settings page at www.example.com/notifications/personal/[username].

Sending the notifications using your own method

Besides registering the notification method, you also need to register a handler that takes care of actually sending the SMS notifications. This happens with the 'send', 'notification:[method]' hook.

Example:

/**
 * Initialize the plugin
 */
function sms_notifications_init () {
        elgg_register_notification_method('sms');
        elgg_register_plugin_hook_handler('send', 'notification:sms', 'sms_notifications_send');
}

/**
 * Send an SMS notification
 *
 * @param string $hook   Hook name
 * @param string $type   Hook type
 * @param bool   $result Has anyone sent a message yet?
 * @param array  $params Hook parameters
 * @return bool
 * @access private
 */
function sms_notifications_send($hook, $type, $result, $params) {
        /* @var Elgg_Notifications_Notification $message */
        $message = $params['notification'];

        $recipient = $message->getRecipient();

        if (!$recipient || !$recipient->mobile) {
                return false;
        }

        // (A pseudo SMS API class)
        $sms = new SmsApi();

        return $sms->send($recipient->mobile, $message->body);
}

Subscriptions

In most cases Elgg core takes care of handling the subscriptions, so notification plugins don’t usually have to alter them.

Subscriptions can however be:

It’s possible to modify the recipients of a notification dynamically with the 'get', 'subscriptions' hook.

Example:

/**
 * Initialize the plugin
 */
function discussion_init() {
        elgg_register_plugin_hook_handler('get', 'subscriptions', 'discussion_get_subscriptions');
}

/**
 * Get subscriptions for group notifications
 *
 * @param string $hook          'get'
 * @param string $type          'subscriptions'
 * @param array  $subscriptions Array containing subscriptions in the form
 *                       <user guid> => array('email', 'site', etc.)
 * @param array  $params        Hook parameters
 * @return array
 */
function discussion_get_subscriptions($hook, $type, $subscriptions, $params) {
        $reply = $params['event']->getObject();

        if (!elgg_instanceof($reply, 'object', 'discussion_reply')) {
                return $subscriptions;
        }

        $group_guid = $reply->getContainerEntity()->container_guid;
        $group_subscribers = elgg_get_subscriptions_for_container($group_guid);

        return ($subscriptions + $group_subscribers);
}

E-mail attachments

notify_user() or enqueued notifications support attachments for e-mail notifications if provided in $params. To add one or more attachments add a key attachments in $params which is an array of the attachments. An attachment should be in one of the following formats:

  • An ElggFile which points to an existing file
  • An array with the file contents
  • An array with a filepath
// this example is for notify_user()
$params['attachments'] = [];

// Example of an ElggFile attachment
$file = new \ElggFile();
$file->owner_guid = <some owner_guid>;
$file->setFilename('<some filename>');

$params['attachments'][] = $file;

// Example of array with content
$params['attachments'][] = [
        'content' => 'The file content',
        'filename' => 'test_file.txt',
        'type' => 'text/plain',
];

// Example of array with filepath
// 'filename' can be provided, if not basename() of filepath will be used
// 'type' can be provided, if not will try a best guess
$params['attachments'][] = [
        'filepath' => '<path to a valid file>',
];

notify_user($to_guid, $from_guid, $subject, $body, $params);