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Description:

powersync attachments helper

PowerSync Attachments Helper for Dart/Flutter #
PowerSync Attachments Helper is a package that assist in keeping files in sync with local and remote storage.
Features #

Handles syncing uploads, downloads and deletes between local and remote storage.

Getting started #
import 'dart:async';
import 'package:powersync_attachments_helper/powersync_attachments_helper.dart';
import 'package:powersync/powersync.dart';

// Set up schema with an id field that can be used in watchIds().
// In this case it is photo_id
const schema = Schema([
Table('users', [Column.text('name'), Column.text('photo_id')])
]);

// Assume PowerSync database is initialized elsewhere
late PowerSyncDatabase db;
// Assume remote storage is implemented elsewhere
late AbstractRemoteStorageAdapter remoteStorage;
late PhotoAttachmentQueue attachmentQueue;

class PhotoAttachmentQueue extends AbstractAttachmentQueue {
PhotoAttachmentQueue(db, remoteStorage)
: super(db: db, remoteStorage: remoteStorage);

// This will create an item on the attachment queue to UPLOAD an image
// to remote storage
@override
Future<Attachment> saveFile(String fileId, int size, {mediaType = 'image/jpeg'}) async {
String filename = '$fileId.jpg';
Attachment photoAttachment = Attachment(
id: fileId,
filename: filename,
state: AttachmentState.queuedUpload.index,
mediaType: mediaType,
localUri: getLocalFilePathSuffix(filename),
size: size,
);

return attachmentsService.saveAttachment(photoAttachment);
}

// This will create an item on the attachment queue to DELETE a file
// in local and remote storage
@override
Future<Attachment> deleteFile(String fileId) async {
String filename = '$fileId.jpg';
Attachment photoAttachment = Attachment(
id: fileId,
filename: filename,
state: AttachmentState.queuedDelete.index);

return attachmentsService.saveAttachment(photoAttachment);
}

// This watcher will handle adding items to the queue based on
// a users table element receiving a photoId
@override
StreamSubscription<void> watchIds({String fileExtension = 'jpg'}) {
return db.watch('''
SELECT photo_id FROM users
WHERE photo_id IS NOT NULL
''').map((results) {
return results.map((row) => row['photo_id'] as String).toList();
}).listen((ids) async {
List<String> idsInQueue = await attachmentsService.getAttachmentIds();
List<String> relevantIds =
ids.where((element) => !idsInQueue.contains(element)).toList();
syncingService.processIds(relevantIds, fileExtension);
});
}
}

// Use this in your main.dart to setup and start the queue
initializeAttachmentQueue(PowerSyncDatabase db) async {
attachmentQueue = PhotoAttachmentQueue(db, remoteStorage);
await attachmentQueue.init();
}
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See our Supabase Flutter To-Do List example app for a concrete implementation of the above.