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PageUpdater

This document provides an overview of the usage of PageUpdater and DerivedPageDataUpdater.

<tt>PageUpdater</tt>

PageUpdater is the canonical way to create page revisions, that is, to perform edits.

PageUpdater is a stateful, handle-like object that allows new revisions to be created on a given wiki page using the saveRevision() method. PageUpdater provides setters for defining the new revision's content as well as meta-data such as change tags. saveRevision() stores the new revision's primary content and metadata, and triggers the necessary updates to derived secondary data and cached artifacts e.g. in the ParserCache and the CDN layer, using a DerivedPageDataUpdater.

PageUpdater instances follow the below life cycle, defined by a number of methods:

                        +----------------------------+
                        |                            |
                        |             new            |
                        |                            |
                        +------|--------------|------+
                               |              |
          grabParentRevision()-|              |
          or hasEditConflict()-|              |
                               |              |
                      +--------v-------+      |
                      |                |      |
                      |  parent known  |      |
                      |                |      |
Enables---------------+--------|-------+      |
  safe operations based on     |              |-saveRevision()
  the parent revision, e.g.    |              |
  section replacement or       |              |
  edit conflict resolution.    |              |
                               |              |
                saveRevision()-|              |
                               |              |
                        +------v--------------v------+
                        |                            |
                        |      creation committed    |
                        |                            |
Enables-----------------+----------------------------+
  wasSuccess()
  isUnchanged()
  isNew()
  getState()
  getNewRevision()
  etc.

The stateful nature of PageUpdater allows it to be used to safely perform transformations that depend on the new revision's parent revision, such as replacing sections or applying 3-way conflict resolution, while protecting against race conditions using a compare-and-swap (CAS) mechanism: after calling code used the grabParentRevision() method to access the edit's logical parent, PageUpdater remembers that revision, and ensure that that revision is still the page's current revision when performing the atomic database update for the revision's primary meta-data when saveRevision() is called. If another revision was created concurrently, saveRevision() will fail, indicating the problem with the "edit-conflict" code in the status object.

Typical usage for programmatic revision creation (with $page being a WikiPage as of 1.32, to be replaced by a repository service later):

$updater = $page->newPageUpdater( $user );
$updater->setContent( SlotRecord::MAIN, $content );
$updater->setRcPatrolStatus( RecentChange::PRC_PATROLLED );
$newRev = $updater->saveRevision( $comment );
const PRC_PATROLLED
$content
Definition: router.php:76

Usage with content depending on the parent revision

$updater = $page->newPageUpdater( $user );
$parent = $updater->grabParentRevision();
$content = $parent->getContent( SlotRecord::MAIN )->replaceSection( $section, $sectionContent );
$updater->setContent( SlotRecord::MAIN, $content );
$newRev = $updater->saveRevision( $comment, EDIT_UPDATE );
const EDIT_UPDATE
Definition: Defines.php:127

In both cases, all secondary updates will be triggered automatically.

<tt>DerivedPageDataUpdater</tt>

DerivedPageDataUpdater is a stateful, handle-like object that caches derived data representing a revision, and can trigger updates of cached copies of that data, e.g. in the links tables, page_props, the ParserCache, and the CDN layer.

DerivedPageDataUpdater is used by PageUpdater when creating new revisions, but can also be used independently when performing meta data updates during undeletion, import, or when puring a page. It's a stepping stone on the way to a more complete refactoring of WikiPage.

NOTE: Avoid direct usage of DerivedPageDataUpdater. In the future, we want to define interfaces for the different use cases of DerivedPageDataUpdater, particularly providing access to post-PST content and ParserOutput to callbacks during revision creation, which currently use WikiPage::prepareContentForEdit, and allowing updates to be triggered on purge, import, and undeletion, which currently use WikiPage::doEditUpdates() and Content::getSecondaryDataUpdates().

The primary reason for DerivedPageDataUpdater to be stateful is internal caching of state that avoids the re-generation of ParserOutput and re-application of pre-save-transformations (PST).

DerivedPageDataUpdater instances follow the below life cycle, defined by a number of methods:

                     +---------------------------------------------------------------------+
                     |                                                                     |
                     |                                 new                                 |
                     |                                                                     |
                     +---------------|------------------|------------------|---------------+
                                     |                  |                  |
               grabCurrentRevision()-|                  |                  |
                                     |                  |                  |
                         +-----------v----------+       |                  |
                         |                      |       |-prepareContent() |
                         |    knows current     |       |                  |
                         |                      |       |                  |
Enables------------------+-----|-----|----------+       |                  |
  pageExisted()                |     |                  |                  |
  wasRedirect()                |     |-prepareContent() |                  |-prepareUpdate()
                               |     |                  |                  |
                               |     |    +-------------v------------+     |
                               |     |    |                          |     |
                               |     +---->        has content       |     |
                               |          |                          |     |
Enables------------------------|----------+--------------------------+     |
  isChange()                   |                              |            |
  isCreation()                 |-prepareUpdate()              |            |
  getSlots()                   |              prepareUpdate()-|            |
  getTouchedSlotRoles()        |                              |            |
  getCanonicalParserOutput()   |                  +-----------v------------v-----------------+
                               |                  |                                          |
                               +------------------>                 has revision             |
                                                  |                                          |
Enables-------------------------------------------+------------------------|-----------------+
  updateParserCache()                                                      |
  runSecondaryDataUpdates()                                                |-doUpdates()
                                                                           |
                                                               +-----------v---------+
                                                               |                     |
                                                               |     updates done    |
                                                               |                     |
                                                               +---------------------+
  • grabCurrentRevision() returns the logical parent revision of the target revision. It is guaranteed to always return the same revision for a given DerivedPageDataUpdater instance. If called before prepareUpdate(), this fixates the logical parent to be the page's current revision. If called for the first time after prepareUpdate(), it returns the revision passed as the 'oldrevision' option to prepareUpdate(), or, if that wasn't given, the parent of $revision parameter passed to prepareUpdate().
  • prepareContent() is called before the new revision is created, to apply pre-save-transformation (PST) and allow subsequent access to the canonical ParserOutput of the revision. getSlots() and getCanonicalParserOutput() as well as getSecondaryDataUpdates() may be used after prepareContent() was called. Calling prepareContent() with the same parameters again has no effect. Calling it again with mismatching parameters, or calling it after prepareUpdate() was called, triggers a LogicException.
  • prepareUpdate() is called after the new revision has been created. This may happen right after the revision was created, on the same instance on which prepareContent() was called, or later (possibly much later), on a fresh instance in a different process, due to deferred or asynchronous updates, or during import, undeletion, purging, etc. prepareUpdate() is required before a call to doUpdates(), and it also enables calls to getSlots() and getCanonicalParserOutput() as well as getSecondaryDataUpdates(). Calling prepareUpdate() with the same parameters again has no effect. Calling it again with mismatching parameters, or calling it with parameters mismatching the ones prepareContent() was called with, triggers a LogicException.
  • getSecondaryDataUpdates() returns DataUpdates that represent derived data for the revision. These may be used to update such data, e.g. in ApiPurge, RefreshLinksJob, and the refreshLinks script.
  • doUpdates() triggers the updates defined by getSecondaryDataUpdates(), and also causes updates to cached artifacts in the ParserCache, the CDN layer, etc. This is primarily used by PageUpdater, but also by UndeletePage during undeletion, and when importing revisions from XML. doUpdates() can only be called after prepareUpdate() was used to initialize the DerivedPageDataUpdater instance for a specific revision. Calling it before prepareUpdate() is called raises a LogicException.

A DerivedPageDataUpdater instance is intended to be re-used during different stages of complex update operations that often involve callbacks to extension code via MediaWiki's hook mechanism, or deferred or even asynchronous execution of Jobs and DeferredUpdates. Since these mechanisms typically do not provide a way to pass a DerivedPageDataUpdater directly, WikiPage::getDerivedDataUpdater() has to be used to obtain a DerivedPageDataUpdater for the update currently in progress - re-using the same DerivedPageDataUpdater if possible avoids re-generation of ParserOutput objects and other expensively derived artifacts.

This mechanism for re-using a DerivedPageDataUpdater instance without passing it directly requires a way to ensure that a given DerivedPageDataUpdater instance can actually be used in the calling code's context. For this purpose, WikiPage::getDerivedDataUpdater() calls the isReusableFor() method on DerivedPageDataUpdater, which ensures that the given instance is applicable to the given parameters. In other words, isReusableFor() predicts whether calling prepareContent() or prepareUpdate() with a given set of parameters will trigger a LogicException. In that case, WikiPage::getDerivedDataUpdater() creates a fresh DerivedPageDataUpdater instance.