Edgewall Software

This page was a draft. See TracDev/NotificationApi page now.

The Open questions section might still contain unimplemented ideas.

Trac Notification API


(since Trac 0.7, deprecated since Trac 1.1.3)

The original notification API consisted mainly of a class hierarchy:

  • Notify (abstract base class for notifications based on a plain text template)
    • NotifyEmail (abstract base class for notifications via plain text email)
      • TicketNotifyEmail (concrete class for ticket notification emails)
      • BatchTicketNotifyEmail (concrete class for ticket batch modification notification emails)

In any situation that required sending notifications, a new instance of such a class was created, invoked once, and discarded. When invoked the object was responsible for finding the recipients, formatting the message and sending the email, all according to various configuration options.

This API turned out to be too inflexible. There are too few extension points that would allow plugins to hook into this process. New subclasses could be defined to handle new situations, but existing code would still explicitly use the original TicketNotifyEmail. Strong inter-dependencies between the multiple levels of inheritance also make overriding certain things unexpectedly difficult.

The only extension point was IEmailSender, a low-level backend for sending an already finalized email. (Since Trac 0.12)

There was also a NotificationSystem component, mainly containing the various configuration option definitions.


(since Trac 1.1.3)

The new API keeps the IEmailSender extension point entirely and the NotificationSystem component almost unchanged, but deprecates the entire Notify hierarchy.

It is replaced by a new class hierarchy. An instance of such a class contains all known data about an event that requires sending notifications:

The NotificationSystem gains some simple methods to process such events. Also several new extension points are introduced that allow plugins to hook into that processing.


Contains the following properties:

  • realm: a string of the affected resource realm (e.g. 'ticket' or 'wiki')
  • category: a string to identify the category of event (e.g. 'created', 'changed' or 'deleted')
  • target: the resource model (e.g. an instance of Ticket or WikiPage) or None
  • time: the datetime when the event happened
  • author: the session id of the user responsible for the event


  • realm is 'ticket'.
  • Known values for category are 'created', 'changed', 'attachment added' and 'attachment deleted'.
  • target is an instance of Ticket.
  • Additional properties:
    • comment: a string containing the user's comment (or None)
    • changes: an empty dictionary for now
    • attachment: None for now


  • realm is 'ticket'.
  • category is 'batchmodify'.
  • target is a list of ticket ids(!)
  • Additional properties:
    • comment: a string containing the user's comment
    • new_values: a dictionary with property names as keys and new property values as values.
    • action: a ticket action controller action

Open Questions

Config options?

Should new config options be defined on the NotificationSystem component as before? Or should they be defined locally in the components where they are used?

Should the values be accessed using e.g. config.getbool() or using NotificationSystem(env).option_name?

How conservative should we be in adding new options, and in breaking backward compatibility?


Should the event classes just be "dumb" data records? Or should the new NotificationSystem methods be moved there?

Is the new class hierarchy useful? Or not needed? Would a simple dictionary be sufficient?

Which properties exactly should be defined? Which ones should be removed or tweaked?

Should the RenderingContext system be considered here? Should a NotificationEvent be (similar to) a RenderingContext?

Batch events?

How should batch events be modeled? Announcer does not implement this feature so no precedent exists.

Should the event.target be:

  • A list of ticket id's?
  • A list of Ticket model instances?
  • A list of TicketChangeEvent instances?
  • None
Last modified 9 years ago Last modified on Dec 6, 2014, 1:30:52 PM
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