Storing Preferences

OpenSRP2 uses the Preferences DataStore and Proto DataStore to store preferences data. Primitive types are stored in the Preferences DataStore and structured types are stored in the Proto DataStore.

The interfaces exposing access to these two storage options are located in engine/datastore/PreferenceDataStore and engine/datastore/ProtoDataStore.

PreferenceDataStore

To register a key-value pair that you intend to store in the preferences datastore, add a key that enforces the type of data being stored and the name of the key in the Keys companion object.

The read() method returns a flow. To observe the flow, call the function in the view model and store the resulting flow. You may then convert it to a StateFlow and expose it to the UI.

The write() method can be used in the UI directly but it is preferable to expose it through a view model to follow the MVVM pattern.

Both read() and write() are Generic methods.

ProtoDataStore

Proto DataStore allows us to store objects in a type-safe way. For ease of adaptation, we use Kotlinx serialization to allow us to use Kotlin data classes instead of Protobuf files to define the schema of the data being stored.

Preferably, any objects made within fhircore with the intent of being persisted in the Proto DataStore should be annotated with @Serializable.

You also need to register a serializer that will serialize and deserialize the object stored within a JSON file on the device. The serializers are found within engine/datastore/serializers.