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->getDisplayName()), $owner->language);

// Body of the notification message
$body = elgg_echo('ratings:notification:body', array(
        $user->getDisplayName(),
        $owner->getDisplayName(),
        $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 or in the elgg-plugin configuration. 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 \Elgg\Hook $hook 'prepare', 'notification:create:object:photo'

 * @return \Elgg\Notification\Notification
 */
function photos_prepare_notification(\Elgg\Hook $hook) {
    $event = $hook->getParam('event');

    $entity = $event->getObject();
    $owner = $event->getActor();
    $recipient = $hook->getParam('recipient');
    $language = $hook->getParam('language');
    $method = $hook->getParam('method');

    /* @var $notification \Elgg\Notification\Notification */
    $notification = $hook->getValue();

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

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

    // Short summary about the notification
    $notification->summary = elgg_echo('photos:notify:summary', [$entity->getDisplayName()], $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.

Notification salutation and sign-off

Elgg will by default prepend a salutation to all outgoing notification body text. Also a sign-off will be appended. This means you will not need to add text like Hi Admin, or Kind regards, your friendly site administrator to your notifications body. If for some reason you do not need this magic to happen, you can prevent it by setting the notification parameter add_salutation to false. You can do this as part of the parameters in notify_user() or in the prepare, notifications hook. You can change the salutation and sign-off texts in the translations.

You can also customize the salutation by overruling the view notifications/elements/salutation the sign-off can be customized by overruling the view notifications/elements/sign-off.

Notification methods

By default Elgg has three notification methods: email, delayed_email and the bundled site_notifications plugin.

Email

Will send an email notification to to the recipient.

Delayed email

Will save the notifications and deliver them in one bundled email at the interval the recipient has configured (daily or weekly).

The availability of this delivery method can be configured by the site administrator in the Site settings section.

The layout of the bundled email can be customized by overruling the view email/delayed_email/plain_text for the plain text part of the email and email/delayed_email/html for the HTML part of the email.

Site notification

Will show the notification on the site.

Registering a new notification method

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 on 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 \Elgg\Hook $hook 'send', 'notification:sms'
 *
 * @return bool
 * @internal
 */
function sms_notifications_send(\Elgg\Hook $hook) {
        /* @var \Elgg\Notifications\Notification $message */
        $message = $hook->getParam('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:
  • Added using the \ElggEntity::addSubscription() function
  • Removed using the \ElggEntity::removeSubscription() function

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 \Elgg\Hook $hook 'get', 'subscriptions'
 *
 * @return void|array
 */
function discussion_get_subscriptions(\Elgg\Hook $hook) {
        $reply = $hook->getParam('event')->getObject();

        if (!$reply instanceof \ElggDiscussionReply) {
                return;
        }

        $subscriptions = $hook->getValue();

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

        return ($subscriptions + $group_subscribers);
}

Muted notifications

Notifications can be muted in order to no longer receive notifications, for example no longer receive notifications about new comments on a discussion.

In order to mute notifications call \ElggEntity::muteNotifications($user_guid) the $user_guid is defaulted to the current logged in user. This will cause all subscriptions on the entity to be removed and a special flag will be set to know that notifications are muted.

The muting rules are applied after the subscribers of a notification event are requested and are applied for the following entities of the notification event: - the event actor \Elgg\Notifications\NotificationEvent::getActor() - the event object entity \Elgg\Notifications\NotificationEvent::getObject() - the event object container entity \Elgg\Notifications\NotificationEvent::getObject()::getContainerEntity() - the event object owner entity \Elgg\Notifications\NotificationEvent::getObject()::getOwnerEntity()

To unmute the notifications call \ElggEntity::unmuteNotifications($user_guid) the $user_guid is defaulted to the current logged in user.

To check if a user has the notifications muted call \ElggEntity::hasMutedNotifications($user_guid) the $user_guid is defaulted to the current logged in user.

Helper page

A helper page has been added which can be linked (for example in an email footer) to manage muting based on a notification.

The page is required to be signed and use the route notifications:mute which needs: - entity_guid the entity the notification is about - recipient_guid the recipient of the notification

Temporarily disable notifications

Users can temporarily disable all notifications by going to the Notification settings and set a start and end date for the period they don’t wish to receive any notifications.

Notification settings

You can store and retreive notification settings of users with \ElggUser::setNotificationSetting() and \ElggUser::getNotificationSettings().

// Setting a notification preference
// notification method: mail
// notification is enabled
// for the purpose 'group_join' (when omitted this is 'default')
$user->setNotificationSetting('mail', true, 'group_join');

// retrieving the preference
$settings = $user->getNotificationSettings('group_join');
// this wil result in an array with all the current notification methods and their state like:
// [
//      'mail' => true,
//      'site' => false,
//      'sms' => false,
// ]

When a user has no setting yet for a non default purpose the system will fallback to the ‘default’ notification setting.

Notification management

A generic menu hook handler is provided to manage notification subscription and muting. If you wish to make it easy for users to subscribe to your entities register a menu hook on register menu:<menu name>:<entity type>:<entity subtype> with the callback Elgg\Notifications\RegisterSubscriptionMenuItemsHandler make sure an \ElggEntity in $params['entity'] is provided. This will work for most elgg_view_menu() calls.