IFilesMetadata

[ArtificialOwl]

#40676

Introduction

This is a feature that allow any app to store files metadata.

When a file is created or modified, an event is broadcasted so that a listener can:

• request for an identical event, but on the background job process
• set metadata, key and value
• define metadata index
• help building queries to search on an indexed metadata
• help building queries that returns metadata linked to fileid

tasks

• model Metadata
  • store type of metadata (string, int, bool, array, float)
  • serialize/deserialize and import from database
• store metadata,
  • update database only if new data (or truly edited) is available
  • avoid parallel update in database
  • delete metadata based on key
  • delete metadata based on prefix
• index metadata (file id, metadata key, metadata value)
  • generate entries in metadata_index based on value type
• queries
  • helper to left join metadata based on file_id
  • helper to search on metadata key
  • helper to search on metadata value
  • helper to get metadata key and metadata value table field
  • helper to convert row's data to metadata object
• events
  • listener on new file
  • listener on edited file
  • on request, dispatch event on background job process
  • occ metadata:get

How to add metadata from your own app:

lib/AppInfo/Application.php

$context->registerEventListener(MetadataLiveEvent::class, UpdateFilesMetadata::class);
$context->registerEventListener(MetadataBackgroundEvent::class, UpdateFilesMetadata::class);

UpdateFilesMetadata.php

use OCP\EventDispatcher\Event;
use OCP\EventDispatcher\IEventListener;
use OCP\FilesMetadata\Event\MetadataBackgroundEvent;
use OCP\FilesMetadata\Event\MetadataLiveEvent;
class UpdateFilesMetadata implements IEventListener {
public function __construct() {}
public function handle(Event $event): void {
if (!($event instanceof MetadataLiveEvent) &&
!($event instanceof MetadataBackgroundEvent)) {
return;
}
$node = $event->getNode();
// only few files are interesting.
if ($node->getMimetype() !== 'image/jpeg') {
return;
}
// we only work on process initiated as background job, so ask for a re-run later
if ($event instanceof MetadataLiveEvent) {
$event->requestBackgroundJob();
return;
}
$fd = $node->fopen('rb');
if (false === $fd) {
return;
}
try {
$oldBufferSize = stream_set_chunk_size($fd, 1);
$data = @exif_read_data($fd, 'ANY_TAG', true);
stream_set_chunk_size($fd, $oldBufferSize);
// we have exif data in $data, let's index the photo taken date $metadata = $event->getMetadata();
$metadata->setInt('photo-taken', strtotime($data['EXIF']['DateTimeOriginal']), true);
} catch (\Exception $e) {
}
}
}

How to use the (current) QueryHelper

 /** @var ConnectionAdapter $conn */
$conn = \OCP\Server::get(ConnectionAdapter::class);
$qb = $conn->getQueryBuilder();
$qb->select('file.fileid', 'file.path')->from('filecache', 'file');
// linking metadataQuery to existing query builder
$metadataQuery = $this->filesMetadataManager->getMetadataQuery($qb, 'file', 'fileid');
// add metadata to the request's results
$metadataQuery->retrieveMetadata();
// only returns result havin
$metadataQuery->joinIndex('another');
$expr = $qb->expr();
$qb->where(
$expr->lte(
$metadataQuery->getMetadataValueIntField(),
$qb->createNamedParameter(1, IQueryBuilder::PARAM_INT)
)
);
$qb->orderBy($metadataQuery->getMetadataValueIntField(), 'desc');