From 5eb564298a41832d29cbfc9301ecd464588df515 Mon Sep 17 00:00:00 2001 From: Don Turner Date: Thu, 12 May 2022 17:07:09 +0100 Subject: [PATCH] [Arch LJ] Adding details of error handling and data synchronization Change-Id: Ie2141ca75cc487a3106e05e79ddbbc530ac93eb6 --- docs/ArchitectureLearningJourney.md | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/docs/ArchitectureLearningJourney.md b/docs/ArchitectureLearningJourney.md index 9b1619e01..8969a3349 100644 --- a/docs/ArchitectureLearningJourney.md +++ b/docs/ArchitectureLearningJourney.md @@ -163,6 +163,8 @@ Repositories are the public API for other layers, they provide the _only_ way to Data is exposed as data streams. This means each client of the repository must be prepared to react to data changes. Data is not exposed as a snapshot (e.g. `getModel`) because there's no guarantee that it will still be valid by the time it is used. +Reads are performed from local storage as the source of truth, therefore errors are not expected when reading from `Repository` instances. However, errors may occur when trying to reconcile data in local storage with remote sources. For more on error reconciliation, check the data synchronization section below. + _Example: Read a list of authors_ A list of Authors can be obtained by subscribing to `AuthorsRepository::getAuthorsStream` flow which emits `List`. @@ -220,9 +222,16 @@ A repository may depend on one or more data sources. For example, the `OfflineFi -Repositories are also responsible for liaising with any remote data sources. Repositories are syncable (they implement `Syncable`), which means they can synchronize data from a remote data source with a local data source. -This is achieved in the `syncWith` method which takes a `Synchronizer` as a parameter. The `Synchronizer` will keep attempting to sync the repository until it successfully completes. In the case of errors, the sync is retried with exponential backoff. +### Data synchronization + +Repositories are responsible for reconciling data in local storage with remote sources. Once data is obtained from a remote data source it is immediately written to local storage. The updated data is emitted from local storage (Room) into the relevant data stream and received by any listening clients. + +This approach ensures that the read and write concerns of the app are separate and do not interfere with each other. + +In the case of errors during data synchronization, an exponential backoff strategy is employed. This is delegated to `WorkManager` via the `SyncWorker`, an implementation of the `Synchronizer` interface. + +See the `OfflineFirstNewsRepository.syncWith` for an example of data synchronization. ## UI Layer