Domain model

Purpose

Moodle’s Log in as lets a user open any account they can see, for as long as they like. Delegate Account narrows that to explicit pairs of people, each with a period, and records who created, changed and revoked each pair. This model names the concepts behind that decision.

Hierarchy of entities

The vertical position of an entity expresses its importance to the project objective. It is not UML inheritance or composition.

Level	Meaning	Entities	Why they are here
1	Core: the project cannot exist without them	Delegation	The plugin exists to decide, for a pair of users and a moment, whether access is allowed.
2	Structural: depend directly on the core	AuthorisedUser, DelegatedAccount, SessionPermission	A delegation links two accounts and may narrow or widen what the session can do.
3	Detail: qualify or specialise level 2	DelegatedSession, Notification	They happen because of a delegation: the session that uses it and the messages that announce it.
4	Support: catalogues, audit, configuration	SiteLimits, ActivityRecord	They bound and observe delegations without changing their meaning.

Diagrams

Entity dictionary

Entity	Level	Definition	Key attributes	Omitted attributes and why
Delegation	1	The permission of one authorised user to open one account, for a period.	realuserid, delegateduserid, timestart, timeend, timerevoked, notificationmode	Audit columns (usercreated, usermodified, userrevoked, timecreated, timemodified) are in the data model.
AuthorisedUser	2	A person who may open delegated accounts: a site administrator or someone holding local/delegateaccount:use.	Moodle user, capability	It is Moodle’s user, not a table of the plugin.
DelegatedAccount	2	The account that is opened. It must exist, be active and, by default, not be a site administrator.	Moodle user	It is Moodle’s user, not a table of the plugin.
SessionPermission	2	An override of one capability for delegated sessions: allow, prevent or prohibit. It applies to one delegation or, with delegationid 0, to every delegated session of the site.	delegationid, capability, permission
DelegatedSession	3	A Moodle login-as session started through a delegation, marked in $SESSION.	the delegation id	It lives in the session, not in a table.
Notification	3	The message sent to the authorised user, the delegated account or both when a delegation is created or revoked.	action, recipient language	The templates are plugin settings.
SiteLimits	4	The site settings that bound delegations: maximum per person, maximum duration, maximum per bulk action, protection of administrators.	maxdelegationsperuser, maximumdurationdays, maxbulkoperations, protectprivilegedtargets
ActivityRecord	4	An event of Moodle’s standard log written while a delegated session was open, read back by the activity report.	Moodle log row	It is Moodle’s log, not a table of the plugin.

Business rules

ID	Rule	Entities	Source
RN-001	A delegation is active when it is not revoked, its start has been reached and it has no end or the end is in the future.	Delegation	manager::get_delegation_status
RN-002	There is at most one active delegation for a pair of users; revoked ones are kept as history.	Delegation	unique index real_delegated_active_unique
RN-003	Access is checked every time it is requested, not only when the delegation is created: the authorised user must be active and allowed, the delegation must exist, and the target must be an available account.	Delegation, AuthorisedUser, DelegatedAccount	manager::get_delegated_access_error
RN-004	A site administrator cannot be opened as a delegated account unless the protection setting is off.	DelegatedAccount, SiteLimits	manager::protect_privileged_targets
RN-005	An authorised user cannot hold more active delegations than the site limit, and one action cannot create more records than the bulk limit.	Delegation, SiteLimits	manager::get_delegation_limit_error, get_bulk_operation_error
RN-006	A delegated session that stops being valid is ended on its next request.	DelegatedSession	hook\after_config, manager::end_invalid_delegated_session
RN-007	Session permissions apply to the open sessions from their next page, and are re-applied on every request.	SessionPermission, DelegatedSession	session_capabilities::apply

Lifecycles

State diagram of a delegation: entity-states.