adding-sync-resource.md

Adding a new sync resource

Pre-requisites

• A Room table where the data can be synced to and from like BloodSugarMeasurement

Steps

Sync APIs are the ones where we pull from the server and push new records to the server. Although some API might just pull from the server as well. Here we will only talk about the former. Once the API contracts are finalized, we need to start with following to introduce the API in the code. We will use blood sugar APIs as an example here.

1. Start by creating a @JsonClass data class called BloodSugarMeasurementPayload and add the API response payload as per the contract.
2. Add response class BloodSugarPullResponse as follows:

@JsonClass(generateAdapter = true)
data class BloodSugarPullResponse(

   @Json(name = "blood_sugars")
   override val payloads: List<BloodSugarMeasurementPayload>,

   @Json(name = "process_token")
   override val processToken: String

) : DataPullResponse<BloodSugarMeasurementPayload>

3. Save the processToken in a shared preference and provide it through the Dagger DI graph.
4. Create a Retrofit Api interface for adding the HTTP GET and POST requests for pulling and pushing records respectively.
5. Add a new Repository that implements SynceableRepository<T,P>. Use the table BloodSugarMeasurement as T and payload class BloodSugarMeasurementPayload as P. This repository is used as an interface between the API and the database.
6. Implement the overridden methods in the repository class by adding queries in the corresponding Dao. While most of the methods here are backed by straightforward queries, there is one in particular that can be challenging.

override fun mergeWithLocalData(payloads: List<BloodSugarMeasurementPayload>): Completable {
 return payloads
     .toObservable()
     .filter { payload ->
       val localCopy = dao.getOne(payload.uuid)
       localCopy?.syncStatus.canBeOverriddenByServerCopy()
     }
     .map { it.toDatabaseModel(DONE) }
     .toList()
     .flatMapCompletable { Completable.fromAction { dao.save(it) } }
}

7. Introduce a new class that implements ModelSync which will be responsible for syncing. Follow any existing class like BloodPressureSync to implement the overridden methods.