@ -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.
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_
_Example: Read a list of authors_
A list of Authors can be obtained by subscribing to `AuthorsRepository::getAuthorsStream` flow which emits `List<Authors>`.
A list of Authors can be obtained by subscribing to `AuthorsRepository::getAuthorsStream` flow which emits `List<Authors>`.
@ -220,9 +222,16 @@ A repository may depend on one or more data sources. For example, the `OfflineFi
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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.
Don Turner
3 years ago