Events API

Events 2
Project state	Completed
Tracker issue	MDL-39797 , MDL-39952, MDL-39846
Discussion	https://moodle.org/mod/forum/discuss.php?d=229425
Assignee	Backend Team

What are events?

Events are atomic pieces of information describing something that happened in Moodle. Events are primarily the result of user actions, but could also be the result of the cron process or administration actions undertaken via the command line.

When an action takes place, an event is created by a core API or plugin. The Events system then disseminates this event information to observers registered for this event. In this way, the events system acts as a communication backbone throughout the Moodle system. Event observers can not modify event data or interrupt the dispatching of events, it is a one way communication channel.

Why was a new events system needed?

The need to improve the Events system was prompted by a need for a richer and more efficient logging system, however the benefits of this improvement are useful to other parts of Moodle that observe event information.

• The events need to be more strictly defined for logging and other advanced use cases. They need to contain more information, organised in a standardised way (in addition to the fields from the legacy log table and log_actions table).
• Complex data types were allowed in old events, which was causing major problems when serialising/storing/unserialising the data.
• The logging tables and events contain similar information and were triggered at the same places; utilising events for logging would remove this code duplication. All events should be loggable and all current log entries should be triggered as events.
• The logging system is an event observer, listening to all events and directing them to logging storage plugins in a controllable way.
• It is possible to subscribe to '*' event, which would allow a system to potentially observe, and selectively deal with, all events. Previously, handlers did not receive event names which made this problematic.
• Previously, event handlers could trigger exceptions during site upgrades, which would lead to fatal upgrade problems. The new design eliminates this.
• Failure in previous handlers blocked dispatching of subsequent events. Problems in new observers would only be logged and execution would continue normally.
• Previously, execution of external handlers during DB transactions blocked other handlers. This would be eliminated by in-memory buffer for external events.
• Previously there was no observer priority.
• Previously, nested events were not dispatched sequentially, which would change the order of events were received by lower priority handlers.

Performance

Some basic profiling was conducted.

This next two paragraphs need to be replaced with results.

There is a general plan to complete pre- and post-implementation testing as development happens. The new system will be implemented in parallel with the old one, which should help with comparison of new and old logging and event triggering performance on each page.

Our aim is to capture more information about actions in Moodle by triggering more events and logging more information about each event. This is going to impact negatively on performance. We hope to offset that impact by improving log storage, simplifying event dispatching and adding other core performance improvements. The proposed class structure of the base event should allow some new advanced techniques, which may also improve performance in some scenarios.

More details will be added to this section soon.

Events API

Each plugin defines the events that it can report (trigger) by extending an abstract base class, once for each possible event. This approach has several benefits.

Events are active objects

When they are triggered and possibly after they are reinstantiated (say, when they are retrieved from a log), an event object is able to provide callback functions for various purposes (such as event description).

Automatic inclusion

Event class definitions are automatically included when needed, without having to maintain lists of known event types. During development new event definitions and observers can be added without the need to upgrade, only purging of the MUC cache is required.

Maintainability

It is relatively simple to add new events and migrate existing events. Code review is simplified because there is less duplication of code when triggering same events and all event related information/code is concentrated in one file in fixed locations.

Self documenting

The behaviour of events is combined with the definition of events in one place (file). It is easy for event observer writers to know what events a plugin can trigger. This includes support for autocompletion and code inspection in modern IDEs. A list of all events is now available as a report to administrators and researchers.

Quick, self-validating data structure

As events are instantiated objects, the PHP processor will validate the structure and type of event classes. This does not ensure data value validity, but does give some assurance of consistency and it also detects unintentional typos.

Backwards compatibility and migration

Events:

• All legacy events in the standard distribution have been replaced with the new events API and events_trigger() has been deprecated.
• For events that already exist in Moodle 2.5, the additional legacy information has been added to the event data (in properties 'legacyeventname' and 'legacyeventdata')
• The legacy events handling code is maintained separately and will continue being supported in Moodle 2.7.
• All legacy events-handlers have been migrated to new observers in standard distribution.
• In future, more subsystems may be migrated to events-observers, ex.: gradebook history, completion.

Logging:

• The function add_to_log() has been deprecated with a notice as of Moodle 2.7.
• Existing add_to_log() parameters have been migrated to method get_legacy_log_data() in new events. Calls to core_event_base::trigger() will lead to entries being added to the legacy log table if the legacy log plugin is enabled.

See https://docs.moodle.org/dev/Migrating_logging_calls_in_plugins

Event dispatching and observers

The new event dispatching system is completely separate from the old events code. Original event handlers are now called observers with the description stored in the same db/events.php file, but as a new array with a different format.

Event observers

Observers are described in db/events.php in the array $observers, the array is not indexed and contains a list of observers defined as an array with the following properties;

• eventname – fully qualified event class name or "*" indicating all events, ex.: \plugintype_pluginname\event\something_happened.
• callback - PHP callable type.
• includefile - optional. File to be included before calling the observer. Path relative to dirroot.
• priority - optional. Defaults to 0. Observers with higher priority are notified first.
• internal - optional. Defaults to true. Non-internal observers are not called during database transactions, but instead after a successful commit of the transaction.

$observers = array(

    array(
        'eventname'   => '\core\event\sample_executed',
        'callback'    => 'core_event_sample_observer::observe_one',
    ),

    array(
        'eventname'   => '\core\event\sample_executed',
        'callback'    => 'core_event_sample_observer::external_observer',
        'priority'    => 200,
        'internal'    => false,
    ),

    array(
        'eventname'   => '*',
        'callback'    => 'core_event_sample_observer::observe_all',
        'includefile' => null,
        'internal'    => true,
        'priority'    => 9999,
    ),

);

NOTE: Event observers are cached. If you add or change observers you need to purge the caches or they will not be recognised. Plugin developers need to bump up the version number to guarantee that the list of observers is reloaded during upgrade.

Event dispatching

A list of available observers is constructed on the fly directly from all available 'events.php' files from core and all plugins. Previously handlers were installed only during installation and upgrade. This has little risk of performance regression because the list is already cached in MUC. Observers get events before installation or any upgrade, however observers are not notified during the initial installation of Moodle core tables.

Developers of observers must make sure that execution does not end with a fatal error under any condition (before install, before upgrade or normal operation). Exceptions are automatically captured, logged in the PHP error log, and notification of other observers continues. Original handlers could not throw any exceptions at any time.

Observers are notified sequentially in the same order in which events were triggered. This means that events triggered in observers are queued in FIFO buffer and are processed after all observers of the current event are notified.

Differences from old event handling

1. New events contain a lot more structured information.
2. There is a separate record snapshot cache that may be used when deleting data or for observer performance improvements.
3. There is no database access in new event dispatching code.
4. There is no support for delayed cron execution. This eliminates performance problems, simplifies events dispatching and prevents abuse of cron events.
5. Events triggered in observers are processed in a different order.
6. External events are buffered when a transaction is in progress, instead of being sent to the cron queue.
7. It is possible to define multiple observers for one event in one events.php file.
8. It is possible to subscribe an observer to all events.
9. The new event manager is using frankenstyle autoloading, which leads to a smaller memory footprint when events are not used on the current page.

Triggering events

• All event definitions are classes extending the \core\event\base class.
• Events are triggered by creating a new instance of the class event and executing $event->trigger().
• Event class name is a unique identifier of each event.
• Class names and namespace follow the identifier scheme \frankenstyle_component\event\some_object_action. Core events are in namespace '\core\event\'.
• Each event class is defined in a separate file. File name and location must match the class name for the use of auto loading, for example: plugindir/classes/event/something_happened.php
• The event identifier suffix has the form some_object_action (something_happened in the example above) and should follow the standard naming convention. The last word after the underscore is automatically parsed as its action, the rest of word is its object.

Decision: Recommended verb list

Examples: \core\event\course_completed, \mod_assign\event\submission_commented, \mod_forum\event\post_shared, \mod_forum\event\post_responded, etc.

• Ideally, it should be possible to trigger an event without gathering additional information for the event. To reduce the cost of data gathering, specifically the cost of database reads, at least the minimal values needed to trigger an event should be already available in variables.

An example of triggering an event:

$event = \mod_myplugin\event\something_happened::create(array('context' => $context, 'objectid' => YYY, 'other' => ZZZ));
// ... code that may add some record snapshots
$event->trigger();

Use of PHP autoloading

All new OOP APIs in Moodle 2.6 onwards are going to use class auto loading - see Automatic class loading. New events use PHP within strictly defined namespaces, which concentrate all event classes in the classes/event/ subdirectory.

Why separate classes?

Pros

• Maintainability - It is much easier to review, debug and integrate.
• Self documenting, behaviour is combined with definition.
• It is extremely flexible for plugin developers and core devs too.
• Automatic lists events can be generated without being installed - PHPDocs as events documentation.
• It is included only when needed using autoloading.
• Self-validating data structure (by PHP).
• Some developers will find it easier to copy whole class files as templates.

Cons

• Big learning curve for developers without OOP skills (all other new subsystems in Moodle already use OOP, you can not code without these skills any more).
• Some developers may find it harder to copy-and-paste examples because they will need to create new class first and use it afterwards (this can be viewed as a benefit because it forces developers to think more about events).
• This has increased the number lines of code in Moodle for events and logging.

Information contained in events

Events have to contain as much information as they can, but this should not affect the performance. That's why part of the information is available in properties, and the rest via methods. This allows for delayed computation of data until the time it is really needed, if it ever is.

Properties

The following is a list of properties that the developer has to pass to the event upon creation, or ones that can be automatically generated where possible and cost free. Some of these properties are not mandatory.

Property name	Title	Type	Required	Comment
eventname	Event name	static, automatic from class name	-	Automatically computed by copying class name
component	Component	static, automatic from top namespace	-	Component declaring the event, automatically computed from class name.
action	Action	static, automatic from last word in class name	-	Can be automatically computed from class name.
target	target of action	static, automatic from class name	-	Target on which the action is taken, can be automatically computed from class name.
objecttable	Database table name	static	optional (Must be set if objectid present)	Database table name which represents the event object to the best. Never use a relationship table here.
objectid	Object ID	variable	Optional (Must be set if objettable present)	Id of the object record from objecttable.
crud	Transaction type	static	optional	One of [crud] letters - indicating 'c'reate, 'r'ead, 'u'pdate or 'd'elete operation. Statically declared in the event class method init().
level / edulevel	Level	static	optional	Level of educational value of the event. Statically declared in the event class method init(). Changed from level to edulevel in Moodle 2.7 (See below for more details)
contextid	Context ID	mandatory	-
contextlevel	Context level	automatic from context	-	This tells you if it was a course, activity, course category, etc.
contextinstanceid	Context instanceid	automatic from context	-	Based on context level this may be course id , course module id, course category, etc. (event->contextinstanceid)
userid	User ID	defaults to current user	-	User ID, or 0 when not logged in, or -1 when other (System, CLI, Cron, ...)
courseid	Affected course	defaults to course context from context	-	This is used only for contexts at and bellow course level - this can be used to filter events by course (includes all course activities)
relateduserid	Affected user	variable	optional	Is this action related to some user? This could be used for some personal timeline view.
anonymous	Anonymous action	variable	optional (Defaults to 0)	Is this action anonymous? Reports should ignore events with anonymous set to 1.
other	All other data	variable array	optional	Any other fields needed for event description - scalars or arrays, must be serialisable using json_encode(). Floating point numbers cannot be used (see MDL-46701).
timecreated	Time of the event	automatic	-	Time when the event was triggered.

• static: same for all event instances of this class
• variable: might not be same for all instances of this event class
• mandatory: required in order to trigger the event
• optional: not necessarily required to trigger the event

Level property

The edulevel property helps define the educational value of the event. It is intentional that the list is limited to only 3 different constants as having too many options would make it harder for developers to pick the right one(s). We also have to keep in mind that this is not supposed to answer all the questions about a particular event, other event properties like the courseid, the context, the component name can be used with the level to get more granular reports.

Remember that this is event based. If the user that has triggered the event is not really "participating" because he is an admin, or a manager, then it is the job of the report to filter those. In a few cases, the educational level of an event depends on the context (site, course...) and/or the role (admin, teacher...) in these cases the selected educational level should be the most usual use case of that event. The event itself has a static educational level.

Teaching (LEVEL_TEACHING: 1)

Any event/action that is performed by someone (typically a teacher) and has a teaching value (anything that is effecting the learning experience/environment of the students). This should not be combined with "Participating" events.

Valid events:

• A teacher grading a student
• A teacher modifying the course settings
• A teacher adding a new section to the course page
• A teacher modifying a module settings
• A teacher adding a page to course
• A teacher leaving a feedback

INVALID events:

• A teacher posting in a forum (it might affect the learning experience, but not necessarily, so the teacher is just participating)

Participating (LEVEL_PARTICIPATING: 2)

Any event/action that is performed by a user, that is related (or could be related) to his learning experience.

Valid events:

• A user posting to a forum
• A user submitting an assignment
• A user blogging
• A user reading someone's blog
• A user posting a comment
• A user chatting on a chat activity
• A user viewing the course page
• A user deletes a blog post

INVALID events:

• A user updating his profile
• A user visiting someone's profile
• A user viewing his /my/ page
• A user sending a message to another one

Other (LEVEL_OTHER: 0)

Any other action, whether they are related to the site administration, or are specific to user. They do not have any educational value.

Methods

The computation of this data is not required by default, but can be accessed by any event observer if need be.

Method	Comment
get_name()	Returns localised name of the event, it is the same for all instances.
get_description()	Returns non-localised description of one particular event. There are plans to make this localised in future. It is recommended that the string begins with identifying the user who triggered the event by providing the user id in quotations. This applies to other variables used in the description as well. If an activity is also mentioned then the course module id should be used, not the id from the activity table. For example "The user with the id '$this->userid' updated the activity 'youractivity' with the course module id '$this->contextinstanceid'.".
can_view($user)	This method is deprecated, please do not use this.
get_url()	Returns Moodle URL where the event can be observed afterwards. Can be null, if no valid location is present.
get_data()	Returns standardised event data as an array (a good starting point for the information you need to handle an event!)
get_context()	Returns event context
get_legacy_eventname()	Information necessary for event backward compatibility.
get_legacy_eventdata()	Information necessary for event backward compatibility.
get_legacy_logdata()	Information necessary for logging backward compatibility.

Record caching

The standard event data may not contain all the information observers need. The built-in record snapshot support in events allows developers to attach more auxiliary information when triggering events, it may be for example course record, some record that was just deleted, etc.

• Snapshots are expected to be an exact snapshot of the database table at the instance when the event was triggered.
• Snapshot can be set and requested for any table. If not cached, it defaults to direct $DB->get_record calls.
• Please be aware that the snapshots are not stored in the logging subsystem, and cannot be used later when logged event is displayed.
• Snapshot are supposed to be used only by observers. They should never be used by reports or by the event itself.
• When using a snapshot in an observer, please make sure you are taking proper care of handling exceptions as the record you are requesting could have been deleted in the time, in between your observer is notified about the event and the trigger.
• We recommend all delete event must add snapshot of the deleted record.

    $event = \core\event\role_assigned::create(
        array('context'=>$context, 'objectid'=>$ra->roleid, 'relateduserid'=>$ra->userid,
            'other'=>array('id'=>$ra->id, 'component'=>$ra->component, 'itemid'=>$ra->itemid)));
    $event->add_record_snapshot('role_assignments', $ra);
    $event->trigger();

    $event = \core\event\role_unassigned::create(
        array('context'=>$context, 'objectid'=>$ra->roleid, 'relateduserid'=>$ra->userid,
            'other'=>array('id'=>$ra->id, 'component'=>$ra->component, 'itemid'=>$ra->itemid)));
    $event->add_record_snapshot('role_assignments', $ra);
    $event->trigger();

The related methods are:

• public function add_record_snapshot($tablename, $record)
• public function get_record_snapshot($tablename, $id)

Backup/restore

When we perform a restore of an event we may need to map the 'objectid' and 'other' information in order to restore the event accurately. For example - take the event mod_assign\event\feedback_viewed which sets the 'objectid' to the value in the 'assign_grades' table and also stores the 'assignid' in 'other' which represents the id in the 'assign' table. When restoring this we need to map the data to the newly created 'assign_grades' and 'assign' entries as the event will be related to a new assignment, like when restoring to a new course. In order for the mapping to work it is necessary for the event to specify the relationship between these values by defining the static functions get_objectid_mapping() and get_other_mapping(). See the code example below -

public static function get_objectid_mapping() {
    return array('db' => 'assign_grades', 'restore' => 'grade');
}

public static function get_other_mapping() {
    $othermapped = array();
    $othermapped['assignid'] = array('db' => 'assign', 'restore' => 'assign');

    return $othermapped;
}

The 'db' value is the name of the database table the id is linked to, and the 'restore' value is what the item is named during restore. The mapping can be found in the restore code. In this case it is located in mod/assign/backup/moodle2/restore_assign_stepslib.php where we can see the grades are mapped by the following in the function process_assign_grade() -

$this->set_mapping('grade', $oldid, $newitemid, false, null, $this->task->get_old_contextid());

The $othermapped variable is an array of all the values in 'other' that require mapping. It is not necessary to list every single value in this array as they may not be related to a database table - only the ones that require mapping are needed.

If your event does not specify an 'objectid', then the get_objectid_mapping() is not necessary to declare. The same applies if there is no 'other' value. It is also common for 'other' to store data that doesn't need mapping at all, in this case simply declare the function but return false. For example, in mod_assign\event\submission_status_updated it is -

public static function get_other_mapping() {
    // Nothing to map.
    return false;
}

There are some events such as assignsubmission_onlinetext\event\submission_created where mapping is not possible. In this case we assign the value to \core\event\base::NOT_MAPPED.

public static function get_objectid_mapping() {
    // No mapping available for 'assignsubmission_onlinetext'.
    return array('db' => 'assignsubmission_onlinetext', 'restore' => \core\event\base::NOT_MAPPED);
}

This way we can distinguish in the logs which values were not mapped.

Events naming convention

Clear event names help developers when reading what events are triggered, and defining the events properties when defining the event class.

Decision: \<component>\event\<some_object>_<verb>

Technically, the verb should be in past participle form (e.g. created).

Existing events

List of existing events in Moodle code base, along with their 2.5 couterparts.

This list is out of date. For a full list of events check out the Event list report which is located in "Site administration > Reports > Event list" of your Moodle installation (2.7+).

Fully qualified event name	2.5 name	Component	Object	Action (Verb)	Comment
assignsubmission_comments\event\comment_created	-	assignsubmission_comments	comment	created
assignsubmission_comments\event\comment_deleted	-	assignsubmission_comments	comment	deleted
assignsubmission_file\event\assessable_uploaded	assessable_file_uploaded	assignsubmission_file	assessable	uploaded	To be deprecated MDL-35197
assignsubmission_file\event\submission_created	-	assignsubmission_file	submission	created
assignsubmission_file\event\submission_updated	-	assignsubmission_file	submission	updated
assignsubmission_onlinetext\event\assessable_uploaded	assessable_content_uploaded	assignsubmission_onlinetext	assessable	uploaded
assignsubmission_onlinetext\event\submission_created	-	assignsubmission_onlinetext	submission	created
assignsubmission_onlinetext\event\submission_updated	-	assignsubmission_onlinetext	submission	updated
block_comments\event\comment_created	-	block_comments	comment	created
block_comments\event\comment_deleted	-	block_comments	comment	deleted
booktool_exportimscp\event\book_exported	-	booktool_exportimscp	book	exported
booktool_print\event\book_printed	-	booktool_print	book	printed
booktool_print\event\chapter_printed	-	booktool_print	chapter	printed
core\event\assessable_submitted	-	core	assessable	submitted	Abstract class
core\event\assessable_uploaded	-	core	assessable	uploaded	Abstract class
core\event\base	-	core	base	-	Abstract class
core\event\blog_association_created	-	core	blog_association	created
core\event\blog_comment_created	-	core	blog_comment	created
core\event\blog_comment_deleted	-	core	blog_comment	deleted
core\event\blog_entries_viewed	-	core	blog_entries	viewed
core\event\blog_entry_created	blog_entry_added	core	blog_entry	created
core\event\blog_entry_deleted	blog_entry_deleted	core	blog_entry	deleted
core\event\blog_entry_updated	blog_entry_edited	core	blog_entry	updated
core\event\cohort_created	cohort_added	core	cohort	created
core\event\cohort_deleted	cohort_deleted	core	cohort	deleted
core\event\cohort_member_added	cohort_member_added	core	cohort_member	added
core\event\cohort_member_removed	cohort_member_removed	core	cohort_member	removed
core\event\cohort_updated	cohort_updated	core	cohort	updated
core\event\comment_created	-	core	comment	created	Abstract class
core\event\comment_deleted	-	core	comment	deleted	Abstract class
core\event\comments_viewed	-	core	comments	viewed	Abstract class
core\event\content_viewed	-	core	content	viewed	Abstract class
core\event\course_category_created	-	core	course_category	created
core\event\course_category_deleted	course_category_deleted	core	course_category	deleted
core\event\course_category_updated	-	core	course_category	updated
core\event\course_completed	course_completed	core	course	completed
core\event\course_completion_updated	-	core	course_completion	updated
core\event\course_content_deleted	course_content_removed	core	course_content	deleted
core\event\course_created	course_created	core	course	created
core\event\course_deleted	course_deleted	core	course	deleted
core\event\course_module_completion_updated	activity_completion_changed	core	course_module_completion	updated
core\event\course_module_created	mod_created	core	course_module	created
core\event\course_module_deleted	mod_deleted	core	course_module	deleted
core\event\course_module_instance_list_viewed	-	core	course_module_instance_list	viewed	Abstract class
core\event\course_module_instances_list_viewed	-	core	course_module_instances_list	viewed	Abstract class
core\event\course_module_updated	mod_updated	core	course_module	updated
core\event\course_module_viewed	-	core	course_module	viewed	Abstract class
core\event\course_reset_ended	-	core	course_reset	ended
core\event\course_reset_started	-	core	course_reset	started
core\event\course_restored	course_restored	core	course	restored
core\event\course_section_updated	-	core	course_section	updated
core\event\course_updated	course_updated	core	course	updated
core\event\email_failed	-	core	email	failed
core\event\group_created	groups_group_created	core	group	created
core\event\group_deleted	groups_group_deleted	core	group	deleted
core\event\group_member_added	groups_member_added	core	group_member	added
core\event\group_member_removed	groups_member_removed	core	group_member	removed
core\event\group_updated	groups_group_updated	core	group	updated
core\event\grouping_created	groups_grouping_created	core	grouping	created
core\event\grouping_deleted	groups_grouping_deleted	core	grouping	deleted
core\event\grouping_updated	groups_grouping_updated	core	grouping	updated
core\event\manager	-	core	manager	anager
core\event\mnet_access_control_created	-	core	mnet_access_control	created
core\event\mnet_access_control_updated	-	core	mnet_access_control	updated
core\event\note_created	-	core	note	created
core\event\note_deleted	-	core	note	deleted
core\event\note_updated	-	core	note	updated
core\event\notes_viewed	-	core	notes	viewed
core\event\role_allow_assign_updated	-	core	role_allow_assign	updated
core\event\role_allow_override_updated	-	core	role_allow_override	updated
core\event\role_allow_switch_updated	-	core	role_allow_switch	updated
core\event\role_assigned	role_assigned	core	role	assigned
core\event\role_capabilities_updated	-	core	role_capabilities	updated
core\event\role_deleted	-	core	role	deleted
core\event\role_unassigned	role_unassigned	core	role	unassigned
core\event\user_created	user_created	core	user	created
core\event\user_deleted	user_deleted	core	user	deleted
core\event\user_password_updated	user_password_updated	core	user	updated
core\event\user_enrolment_created	user_enrolled	core	user_enrolment	created
core\event\user_enrolment_deleted	user_unenrolled	core	user_enrolment	deleted
core\event\user_enrolment_updated	user_enrol_modified	core	user_enrolment	updated
core\event\user_list_viewed	-	core	user_list	viewed
core\event\user_loggedin	-	core	user	loggedin
core\event\user_loggedinas	-	core	user	loggedinas
core\event\user_loggedout	user_logout	core	user	loggedout
core\event\user_login_failed	-	core	user_login	failed
core\event\user_profile_viewed	-	core	user_profile	viewed
core\event\user_updated	user_updated	core	user	updated
core\event\webservice_function_called	-	core	webservice_function	called
core\event\webservice_login_failed	-	core	webservice_login	failed
core\event\webservice_service_created	-	core	webservice_service	created
core\event\webservice_service_deleted	-	core	webservice_service	deleted
core\event\webservice_service_updated	-	core	webservice_service	updated
core\event\webservice_service_user_added	-	core	webservice_service_user	added
core\event\webservice_service_user_removed	-	core	webservice_service_user	removed
core\event\webservice_token_created	-	core	webservice_token	created
core\event\webservice_token_sent	-	core	webservice_token	sent
logstore_legacy\event\legacy_logged	-	logstore_legacy	legacy	logged
mod_assign\event\all_submissions_downloaded	-	mod_assign	all_submissions	downloaded
mod_assign\event\assessable_submitted	assessable_submitted	mod_assign	assessable	submitted
mod_assign\event\extension_granted	-	mod_assign	extension	granted
mod_assign\event\identities_revealed	-	mod_assign	identities	revealed
mod_assign\event\marker_updated	-	mod_assign	marker	updated
mod_assign\event\statement_accepted	-	mod_assign	statement	accepted
mod_assign\event\submission_created	-	mod_assign	submission	created	Abstract class
mod_assign\event\submission_duplicated	-	mod_assign	submission	duplicated
mod_assign\event\submission_graded	-	mod_assign	submission	graded
mod_assign\event\submission_locked	-	mod_assign	submission	locked
mod_assign\event\submission_status_updated	-	mod_assign	submission_status	updated
mod_assign\event\submission_unlocked	-	mod_assign	submission	unlocked
mod_assign\event\submission_updated	-	mod_assign	submission	updated	Abstract class
mod_assign\event\workflow_state_updated	-	mod_assign	workflow_state	updated
mod_book\event\chapter_created	-	mod_book	chapter	created
mod_book\event\chapter_deleted	-	mod_book	chapter	deleted
mod_book\event\chapter_updated	-	mod_book	chapter	updated
mod_book\event\chapter_viewed	-	mod_book	chapter	viewed
mod_book\event\course_module_instance_list_viewed	-	mod_book	course_module_instance_list	viewed
mod_book\event\course_module_viewed	-	mod_book	course_module	viewed
mod_chat\event\course_module_instance_list_viewed	-	mod_chat	course_module_instance_list	viewed
mod_chat\event\message_sent	-	mod_chat	message	sent
mod_chat\event\sessions_viewed	-	mod_chat	sessions	viewed
mod_choice\event\answer_submitted	-	mod_choice	answer	submitted
mod_choice\event\answer_updated	-	mod_choice	answer	updated
mod_choice\event\course_module_instance_list_viewed	-	mod_choice	course_module_instance_list	viewed
mod_choice\event\course_module_viewed	-	mod_choice	course_module	viewed
mod_choice\event\report_viewed	-	mod_choice	report	viewed
mod_data\event\comment_created	-	mod_data	comment	created
mod_data\event\comment_deleted	-	mod_data	comment	deleted
mod_data\event\course_module_instance_list_viewed	-	mod_data	course_module_instance_list	viewed
mod_data\event\course_module_viewed	-	mod_data	course_module	viewed
mod_data\event\field_created	-	mod_data	field	created
mod_data\event\field_deleted	-	mod_data	field	deleted
mod_data\event\field_updated	-	mod_data	field	updated
mod_data\event\record_created	-	mod_data	record	created
mod_data\event\record_deleted	-	mod_data	record	deleted
mod_data\event\record_updated	-	mod_data	record	updated
mod_data\event\template_updated	-	mod_data	template	updated
mod_data\event\template_viewed	-	mod_data	template	viewed
mod_feedback\event\course_module_instance_list_viewed	-	mod_feedback	course_module_instance_list	viewed
mod_feedback\event\course_module_viewed	-	mod_feedback	course_module	viewed
mod_feedback\event\response_deleted	-	mod_feedback	response	deleted
mod_feedback\event\response_submitted	-	mod_feedback	response	submitted
mod_folder\event\course_module_instance_list_viewed	-	mod_folder	course_module_instance_list	viewed
mod_folder\event\course_module_viewed	-	mod_folder	course_module	viewed
mod_folder\event\folder_updated	-	mod_folder	folder	updated
mod_forum\event\assessable_uploaded	assessable_content_uploaded	mod_forum	assessable	uploaded
mod_forum\event\course_module_instance_list_viewed	-	mod_forum	course_module_instance_list	viewed
mod_forum\event\course_searched	-	mod_forum	course	searched
mod_forum\event\discussion_created	-	mod_forum	discussion	created
mod_forum\event\discussion_deleted	-	mod_forum	discussion	deleted
mod_forum\event\discussion_moved	-	mod_forum	discussion	moved
mod_forum\event\discussion_updated	-	mod_forum	discussion	updated
mod_forum\event\discussion_viewed	-	mod_forum	discussion	viewed
mod_forum\event\forum_viewed	-	mod_forum	forum	viewed
mod_forum\event\post_created	-	mod_forum	post	created
mod_forum\event\post_deleted	-	mod_forum	post	deleted
mod_forum\event\post_updated	-	mod_forum	post	updated
mod_forum\event\readtracking_disabled	-	mod_forum	readtracking	disabled
mod_forum\event\readtracking_enabled	-	mod_forum	readtracking	enabled
mod_forum\event\subscribers_viewed	-	mod_forum	subscribers	viewed
mod_forum\event\subscription_created	-	mod_forum	subscription	created
mod_forum\event\subscription_deleted	-	mod_forum	subscription	deleted
mod_forum\event\userreport_viewed	-	mod_forum	userreport	viewed
mod_glossary\event\comment_created	-	mod_glossary	comment	created
mod_glossary\event\comment_deleted	-	mod_glossary	comment	deleted
mod_lesson\event\course_module_instance_list_viewed	-	mod_lesson	course_module_instance_list	viewed
mod_lesson\event\course_module_viewed	-	mod_lesson	course_module	viewed
mod_lesson\event\essay_assessed	-	mod_lesson	essay	assessed
mod_lesson\event\essay_attempt_viewed	-	mod_lesson	essay_attempt	viewed
mod_lesson\event\highscore_added	-	mod_lesson	highscore	added
mod_lesson\event\highscores_viewed	-	mod_lesson	highscores	viewed
mod_lesson\event\lesson_ended	-	mod_lesson	lesson	ended
mod_lesson\event\lesson_started	-	mod_lesson	lesson	started
mod_lti\event\course_module_instance_list_viewed	-	mod_lti	course_module_instance_list	viewed
mod_lti\event\course_module_viewed	-	mod_lti	course_module	viewed
mod_lti\event\unknown_service_api_called	lti_unknown_service_api_call	mod_lti	unknown_service_api	called
mod_page\event\course_module_instance_list_viewed	-	mod_page	course_module_instance_list	viewed
mod_page\event\course_module_viewed	-	mod_page	course_module	viewed
mod_quiz\event\attempt_abandoned	quiz_attempt_abandoned	mod_quiz	attempt	abandoned
mod_quiz\event\attempt_becameoverdue	quiz_attempt_overdue	mod_quiz	attempt	becameoverdue
mod_quiz\event\attempt_started	quiz_attempt_started	mod_quiz	attempt	started
mod_quiz\event\attempt_submitted	quiz_attempt_submitted	mod_quiz	attempt	submitted
mod_resource\event\course_module_instance_list_viewed	-	mod_resource	course_module_instance_list	viewed
mod_resource\event\course_module_viewed	-	mod_resource	course_module	viewed
mod_scorm\event\attempt_deleted	-	mod_scorm	attempt	deleted
mod_scorm\event\course_module_instance_list_viewed	-	mod_scorm	course_module_instance_list	viewed
mod_scorm\event\course_module_viewed	-	mod_scorm	course_module	viewed
mod_scorm\event\interactions_viewed	-	mod_scorm	interactions	viewed
mod_scorm\event\report_viewed	-	mod_scorm	report	viewed
mod_scorm\event\sco_launched	-	mod_scorm	sco	launched
mod_scorm\event\tracks_viewed	-	mod_scorm	tracks	viewed
mod_scorm\event\user_report_viewed	-	mod_scorm	user_report	viewed
mod_url\event\course_module_instance_list_viewed	-	mod_url	course_module_instance_list	viewed
mod_url\event\course_module_viewed	-	mod_url	course_module	viewed
mod_wiki\event\comment_created	-	mod_wiki	comment	created
mod_wiki\event\comment_deleted	-	mod_wiki	comment	deleted
mod_wiki\event\comments_viewed	-	mod_wiki	comments	viewed
mod_wiki\event\course_module_instance_list_viewed	-	mod_wiki	course_module_instance_list	viewed
mod_wiki\event\course_module_viewed	-	mod_wiki	course_module	viewed
mod_wiki\event\page_created	-	mod_wiki	page	created
mod_wiki\event\page_deleted	-	mod_wiki	page	deleted
mod_wiki\event\page_diff_viewed	-	mod_wiki	page_diff	viewed
mod_wiki\event\page_history_viewed	-	mod_wiki	page_history	viewed
mod_wiki\event\page_locks_deleted	-	mod_wiki	page_locks	deleted
mod_wiki\event\page_map_viewed	-	mod_wiki	page_map	viewed
mod_wiki\event\page_updated	-	mod_wiki	page	updated
mod_wiki\event\page_version_deleted	-	mod_wiki	page_version	deleted
mod_wiki\event\page_version_restored	-	mod_wiki	page_version	restored
mod_wiki\event\page_version_viewed	-	mod_wiki	page_version	viewed
mod_wiki\event\page_viewed	-	mod_wiki	page	viewed
mod_workshop\event\assessable_uploaded	assessable_content_uploaded	mod_workshop	assessable	uploaded
mod_workshop\event\assessment_evaluated	-	mod_workshop	assessment	evaluated
mod_workshop\event\assessment_evaluations_reset	-	mod_workshop	assessment_evaluations	reset
mod_workshop\event\assessment_reevaluated	-	mod_workshop	assessment	reevaluated
mod_workshop\event\course_module_viewed	workshop_viewed	mod_workshop	course_module	viewed
mod_workshop\event\instances_list_viewed	-	mod_workshop	instances_list	viewed
mod_workshop\event\phase_switched	-	mod_workshop	phase	switched
mod_workshop\event\submission_assessed	-	mod_workshop	submission	assessed
mod_workshop\event\submission_created	-	mod_workshop	submission	created
mod_workshop\event\submission_reassessed	-	mod_workshop	submission	reassessed
mod_workshop\event\submission_updated	-	mod_workshop	submission	updated
mod_workshop\event\submission_viewed	-	mod_workshop	submission	viewed
report_log\event\content_viewed	-	report_log	content	viewed
report_loglive\event\content_viewed	-	report_loglive	content	viewed
report_outline\event\content_viewed	-	report_outline	content	viewed
report_participation\event\content_viewed	-	report_participation	content	viewed
report_stats\event\content_viewed	-	report_stats	content	viewed

Verb list

All events must use a verb from this list. New verbs can be added to this list if required, but additions should only be made if there is no valid alternative (we want to keep this list as small as possible).

verb	Explanation	Source
abandoned	When a attempt is abandoned by user (Quiz attempt)	Moodle
accepted	Example: Accepting a statement when submitting an assignment.	Moodle
added	Used to represent "something that already exists is now part of/bound to another entity". Examples: "Admin added role to user X", "Admin added user X to group A". Wrong example: "User added course in category" because it is a 'move' action, except if a course can be part of multiple categories. The good examples work because: A user can have multiple roles, a user can be in multiple groups.	Moodle
answered	Indicates the actor responded to a Question	Tincan
assessed	Some submitted material has been assessed	Moodle
assigned	Assign some privilege or role to user.	Moodle
attempted	Trying to do an activity. Example: attempting a Math class.	Tincan
awarded	ex:-teacher awarded student a badge.	Moodle
backedup	When a backup has been performed.	Moodle
becomeoverdue	When an activity is overdue Example: Quiz attempt is overdue	Moodle
called	When a call to something is made like an API @see unknown_service_api_called.php	Moodle
commented	Offered an opinion or written experience of the activity. Can be used with the learner as the actor or a system as an actor. Comments can be sent from either party with the idea that the other will read and react to the content.	Tincan
completed	To experience the activity in its entirety. Used to affirm the completion of content. This can be simply experiencing all the content, be tied to objectives or interactions, or determined in any other way. Any content that has been initialized, but not yet completed, should be considered incomplete. There is no verb to 'incomplete' an activity, one would void the statement which completes the activity."	Tincan
created	Used to represent "something new has been created".	Moodle
deleted	Used to indicate the object in context was deleted.	Moodle
disabled	When an activity is disabled. Example: forum read tracking disabled.	Moodle
downloaded	When a user download file from user. Example submission/report downloaded.	Moodle
duplicated	For something that has been copied.	Moodle
enabled	When some setting is enabled. Example: forum read tracking enabled.	Moodle
ended	When a process ends. Example: Lesson ended or course reset ended.	Moodle
evaluated	Material has been evaluated.	Moodle
exported	When a report is exported in certain format.	Moodle
failed	Learner did not perform the activity to a level of pre-determined satisfaction. Used to affirm the lack of success a learner experienced within the learning content in relation to a threshold. If the user performed below the minimum to the level of this threshold, the content is 'failed'. The opposite of 'passed'. This is also used in case when message sending is failed.	Tincan
graded	Used to represent an activity was graded.	Moodle
granted	User is granted some extension or capability. Example: extension granted for submission.	Moodle
imported	The act of moving an object into another location or system.	Tincan
launched	When an external object is launched. Try consider started if there is related stopped event.	Moodle
locked	When an activity is locked. Should have a related unlocked event.	Moodle
loggedin/loggedout	For login and logout.	Moodle
loggedinas	If user is logged in as different user. This is used by only one event (user_loggedinas). Adding this verb makes event name more clear, then using loggedin verb.	Moodle
locked		Moodle
moved	Used to indicate the object in context was moved.	Moodle
passed	Used to affirm the success a learner experienced within the learning content in relation to a threshold. If the user performed at a minimum to the level of this threshold, the content is 'passed'. The opposite of 'failed'.	Tincan
printed	Something is printed.	Moodle
reassessed	Submitted material has been assessed again.	Moodle
reevaluated	Material has been evaluated again.	Moodle
removed	By opposition to "Added". This does not mean that the object has been deleted, but removed from the entity, or not bound to it any more.	Moodle
replaced	Similar to "Updated". But when the change does not apply to a clear identifiable identity and somehow is global, broader.	Moodle
reset	Sets one or more properties back to the default value.	Moodle
restored	When restoring a backup. Rolling back to a previous state.	Moodle
revealed	Some identity is revealed. Example: Identities revealed after blind marking.	Moodle
searched	Something is searched. Example: searched in course.	Moodle
sent	Message sent.	Moodle
started	Some activity started	Moodle
submitted	This is very close to "Attempted". Depends on context which one should be used. For example:- "Admin submitted a form. Student attempted a quiz." is correct, however some cases might not be as clear as the previous example. We can say both "Student submitted an assignment" or "student attempted an assignment". We need to make the difference clear.	Moodle
suspended	Suspend something. (example a user)	Tincan (However the context is different)
switched	Something has been switched. For example:- The workshop phase has been switched to assessment"	Moodle
unassigned	As opposed to assigned. When some role is unassigned.	Moodle
unlocked		Moodle
upgraded	Something was upgraded, some module probably	Moodle
updated	Used to indicate the object in context was updated. Simple example is "Admin updated course xyz".	Moodle
uploaded	When an assignment is uploaded.	Moodle
viewed	Something has been viewed. For example:- "Student viewed chapter 1 of book 1."	Moodle

Rules

Use singular

Plurals must be used on objects when it's a One to Many relationship. Ex: bulk import, mass deletion, ... In any other case, use the singular.

Ends with a verb

The last word (after the last underscore) must be a verb.

Consistency among child events

If an event is extending a parent class, it should have the same exact name as the parent event.

Deprecated events

Following are the events that were supported in 2.5, but deprecated in 2.6 or later

groups_groupings_deleted (see MDL-41312)

groups_groupings_groups_removed (see MDL-41312)

groups_groups_deleted (see MDL-41312)

groups_members_removed (see MDL-41312)

Shared events

Decision: Not supported at this stage.

In Moodle 2.5 we have a good example of a shared event: 'assessable_content_uploaded' which is triggered in forum, 'assignment and workshop.

The problem with shared events is that we cannot easily track what component triggered them. Of course we could add a new property to the event to keep track of that, but we would soon need more information and more properties. Also, in the case of a logger, the event received would be unique, where in fact it should be considered different depending on the component firing it.

In our first implementation, we will create one specific event per module. This flexibility does not prevent any observer from capturing them, but still makes sure that the consistency and specificity of each event is maintained.

It could happen that some events are defined in core and shared, but this should not really happen as low-level APIs should trigger the event, and a module should call that low API instead of doing the job itself.

One to many

Decision: Each event should have a one to one relationship. We can reconsider this at a later stage, if the performance hit is extremely high.

In 2.5, some events are triggered when an action happens on multiple objects. We have to decide whether we want to keep supporting One to Many events or not.

Keeping a list of all changes for multiple actions may be problematic because you would have to keep them all in memory until all things are processed. This might also result in the order of events being incorrect. The only correct solution seems to be to trigger each item individually and then many things at the end. Performance needs to be improved elsewhere...

Accuracy

It is important to trigger individual events for each and every action, bulk events are very strongly discouraged because existing observers would not receive important information. Changes from one to many would break backwards compatibility with observers and reporting.

Performance

Triggering one event is cheaper then repeating the same events x number of times...

Information tracking

A bulk event, might not be verbose enough to allow for proper logging afterwards. Though this is the responsibility of the logger, we probably want to make it easy to store relevant information.

Double event

In the case of a bulk user import, if we were to trigger an event per user created, we probably want to trigger one event 'user_bulk_upload_started' when the action starts.

Unit Testing

With unit testing for this system we want to assert the following:

• That event strict validation and custom validation works.
• Missing event data is auto filled with accurate data.
• Typos in properties passed to ::create() are captured (if we decide to validate).
• The legacy methods return the expected values (use assertEventLegacyData() and assertEventLegacyData())
• The class properties are correctly overridden (crud, level, action, object, ...).
• The properties automatically generated (component, name, ...) are correct.
• Events are dispatched to the corresponding observers.
• Events are dispatched to the corresponding legacy handlers.
• Events are dispatched to the * observers.
• Events perform an add_to_log() if it has legacy log data.
• 'Events restore' restored the whole event data, and does not miss any information.
• 'Events restore' does not generate any extra information.
• Event methods should check context object or avoid using it, as context might not be valid at time of event restore (use assertEventContextNotUsed())

PHP docs

• All events php docs must include @since parameter, indicating when the event was first included in standard Moodle distribution.
• All events must declare the $other properties using mark down in the php docs. This later might be converted to a self documenting structure. (See MDL-45108)

/**
 * blog_association_created
 *
 * Class for event to be triggered when a new blog entry is associated with a context.
 *
 * @property-read array $other {
 *      Extra information about event.
 *
 *      - string associatetype: type of blog association, course/coursemodule.
 *      - int blogid: id of blog.
 *      - int associateid: id of associate.
 *      - string subject: blog subject.
 * }
 *
 * @package    core
 * @since      Moodle 2.7
 * @copyright  2013 onwards Ankit Agarwal
 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */

Example events

Assignment

Assumption: Course contains groups with students in each group.

1. Teacher creates an assignment with group mode set to 'Separate groups' and Feedback type set to comments and files.

• Event: User 'Teacher' has created assignment 'B' in course 'C101'.

2. A student views the assignment.

• Event: User 'Student' has viewed assignment 'B' in course 'C101'.

3. A member from one of the groups submits an assignment

• Event: User 'Student' has added a submission for assignment 'B' for group 'C' in course 'C101'.
• Event: Email sent to the teacher and all students in that group.

4. User 'Adrian' adds some changes to the assignment and updates it.

• Event: User 'Adrian' has updated the submission for assignment 'B' for group 'C' in course 'C101'.
• Event: Email sent to the teacher and all students in that group.

5. Teacher views the assignment.

• Event: User 'Teacher' has viewed assignment 'B' in course 'C101'.

6. Teacher clicks on 'View/grade all submissions'

• Event: User 'Teacher' has viewed the assignment 'B' grade area in course 'C101'.

7. Teacher clicks to grade the student's submission.

• Event: User 'Teacher' has viewed the submission for user 'student' for assignment 'B' in course 'C101'.

8. Teacher marks the assignment with the setting 'Apply grades and feedback to entire group' set to 'Yes' leaving a comment and a file.

• Event: User 'Teacher' has marked assignment 'B' for group 'C' in course 'C101'.
• Event: User 'Teacher' has left a comment for assignment 'B' for group 'C' in course 'C101'.
• Event: User 'Teacher' has uploaded a feedback file for assignment 'B' for group 'C' in course 'C101'.
• Event: User 'Teacher' has uploaded a file to the course 'C101'.
• Event: Email sent to user 'Student' notifying them their submission for assignment 'B' has been marked. - This is done for all users in the group.

9. User 'Adrian' views the feedback.

• Event: User 'Adrian' has viewed assignment 'B' in course 'C101'.

10. User 'Adrian' opens the feedback file.

• Event: User 'Adrian' has viewed the file 'A' for assignment 'B' in course 'C101'.

11. User 'Adrian' adds some changes to the assignment insulting the teachers marking and updates it.

• Event: User 'Adrian' has updated the submission for assignment 'B' for group 'C' in course 'C101'.
• Event: Email sent to user 'Teacher' notifying them that user 'Adrian' has updated the submission for assignment 'B'.
• Event: Email sent to user 'Student' notifying them their submission for assignment 'B' has been updated. - This is done for all users in the group.

12. The teacher clicks directly on the link in the email to be taken to the grading page.

• Event: User 'Teacher' has viewed the submission for user 'student' for assignment 'B' in course 'C101'.

13. The teacher is upset due to the harsh comments and decides to mark Adrian down, but not the rest of the group by setting 'Apply grades and feedback to entire group' set to 'No'.

• Event: User 'Teacher' has marked assignment 'B' for user 'Adrian' in course 'C101'.
• Event: User 'Teacher' has left a comment for assignment 'B' for user 'Adrian' in course 'C101'.
• Event: User 'Teacher' has uploaded a feedback file for assignment 'B' for user 'Adrian' in course 'C101'.
• Event: Email sent to user 'Adrian' notifying them their submission for assignment 'B' has been marked.

FAQs

Why not create events in core subsystems?

Because we could not see all core events in one place, it would create problems when naming event classes and finally subsystems are incomplete, we would have to add more now because we could not move the events in the future.

Possible future work

• MDL-45108 "Other" parameters should be defined in a method similar to webservices
• MDL-45217 Create traits for refactoring event triggers
• MDL-42897 Converting completion to use events
• MDL-42898 Develop a timeline page/block

See Also

Logging 2

Tin Can