COmanage Registry can track each change made to a Model through the use of Changelogs. When a record is modified, the old values are archived in order to provide an audit or change log of the modifications that were made. Changelogs are implemented using a custom Cake Behavior (ChangelogBehavior).
Changelog Behavior operates using a modified copy on write design. When a record is changed, the old values are copied to a new record, and then the original record is updated with the new values. There are two reasons for this design: it avoids massive rekeying when a record is updated (otherwise related Models would all need to be re-keyed to point to the new record), and because it's tricky within Cake to rewrite the record ID in the middle of an operation. (That is, for /foos/edit/23, Cake really wants the item being edited to be #23, and not some new number.) It is simply easier to make the archived copy the new record.
This behavior can be modified using the model variable $relinkToArchive. If a Model defines a related hasOne or hasMany Model in this variable, then ChangelogBehavior will relink the related model to the archive copy, as part of the afterSave callback. This is useful for maintaining historical context, such as for Petition attribute definitions. If the Model relationship is belongsTo, a similar rewrite happens, but in beforeSave and with the assumption that the parent model is what was changed.
Enabling Changelogs for a Model
As with other Behaviors, the appropriate Model should define $actsAs = ("Changelog") or similar.
In order to support Changelogs, a Changelog-enabled Model must define several fields. As described below, these fields are used to track changed records:
revisiondeletedactor_identifiermodel_id
For performance reasons, model_id should be indexed.
$relinkToArchive should also be defined if needed, as described above.
actor_identifier stores the username (identifier) of whoever made the change. This is a string rather than a foreign key into cm_co_people for several reasons:
- No need for foreign keys and Model relations, which must be added to each Changelog model, and are tricky to automatically create for tables created in
schema.xmlbefore cm_co_people. - Audit integrity is maintained even after an expunge.
- Some models are not attached to a CO, so tracking a CO Person as an actor doesn't quite make sense.
What ChangelogBehavior Does
ChangelogBehavior intercepts find, save, and delete requests to transparently manage the Changelog records.
Save (Add)
revisionis set to 0.author_co_person_idis set to the current CO Person.
Save (Update)
- The prior values are copied to a new row, and
model_idis set to point to the parent record. revisionis incremented.- If the Model defines related models in
$relinkToArchive, those related models will be re-keyed so that the related records point to the archived attribute instead of the current attribute. (By default, related models remain linked to the current attribute.)
Delete
deletedis set to true.
Find
- By default, a find that does not request a specific record ID will be modified to return the most current revision and to exclude deleted records.
- A find with the parameter
archivedset to true will return all records, not just those described above.
Sample Relations
