如何在onComplete（Rxjava2）中使用Observable

Question

I'm writing my application with as much as I can of rxjava and I'm having the following problem.

I Have a method that syncs data with the api, and I download stuff based on a timestamp. So I would like the following data flow:

Get last timestamp -> Download data -> Save data -> Update timestamp if no errors ocurred

The problem is that I receive the timestamp from the api response to avoid date differences between devices, and as soon as I transform the response from the api I loose the timestamp.

Here is a simplification of the current flow:

class Response
{
    Date timeStamp;
    Data data;
}

interface IRepository
{
    Completable insert(Data data);
}

interface IWebService
{
    Observable<Response> getByLastUpdate(Date date);
}

class SyncPreferences
{
    public Date getLastDownloadDate() { /**/ }
    public void setLastDownloadDate(Date date){ /**/ }
}

public class SyncService
{
    private final IRepository repository;
    private final IWebService webService;
    private final SyncPreferences syncPreferences;

    public SyncService(IRepository repository, SyncPreferences syncPreferences, IWebService webService)
   {
        this.repository = repository;
        this.webService = webService;
        this.syncPreferences = syncPreferences;
   }

   private Completable sync()
   {
        return webService.getByLastUpdate(syncPreferences.getLastDownloadDate())
            .doOnComplete((response) -> {
                syncPreferences.setLastDownloadDate(response.timeStamp)
            }) // What I would like to do
            .flatMapCompletable((response) -> {
                repository.insert(response.data);
            });
    }
}

The problem is that doOnComplete method does not receive the parameter ( response ) from the observable and I would like to set the timestamp as the last thing so if an error occurs I can just retry downloading with the old timestamp.

The only solution I found was make a transaction mechanism in the SyncPreferences that I could use like this:

    private Completable sync()
    {
        return webService.getByLastUpdate(syncPreferences.getLastDownloadDate())
            .doOnNext((response) -> {
                syncPreferences.setLastDownloadDate(response.timeStamp);
            })
            .flatMapCompletable((response) -> {
                repository.insert(response.data);
            })
            .andThen(syncPreferences.commitChanges());
    }

I am new to RxJava so if you have suggestions in general I would be glad to know =]

PS I don't know if this code compiles since I just wrote it here for the example.

Answer 1

What about this:

webService.getByLastUpdate(syncPreferences.getLastDownloadDate())
    .flatMapCompletable(response ->
        repository
            .insert(response.data)
            .doOnComplete(() ->
                syncPreferences.setLastDownloadDate(response.timeStamp)
            )
    );