Repository pattern with multiple remote data sources Code Answer

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I started learning Android development rather recently and made the mistake of creating god activities. I then learned about architecture and chose to refactor my existing code into an MVP architecture. So far so good but my next bottleneck is using the repository pattern. I understand that the repository is essentially an abstraction that the presenter calls to get data. It gracefully handles when to use a remote data source or a local data source, caching, etc.

But what if there needed to be multiple data sources? For example, I store and pull most data from Firebase Firestore but for complex querying and searching, I pull data (via REST through Retrofit) from an ElasticSearch instance. Both of these are remote data sources.

As such, instead of having my repository like so:

public class BookRepository implements BookDataSource {

    private final BookDataSource remoteSource;
    private final BookDataSource localSource;

    public BookRepository(@NonNull BookDataSource remoteSource,
                          @NonNull BookDataSource localSource){
        this.remoteSource = remoteSource;
        this.localSource = localSource;
    }
}

It looks something like this:

public class BookRepository implements BookDataSource {

    private final FirebaseFirestore firestore;
    private final Retrofit retrofit;
    private final SomeLocalSource local;

    public BookRepository(@NonNull FirebaseFirestore firestore,
                          @NonNull Retrofit retrofit,
                          @NonNull SomeLocalSource local){
        this.firestore = firestore;
        this.retrofit  = retrofit;
        this.local     = local;
    }
}

As you can see, what I am passing changes the structure and if I were to, in the future, move to a different database, I’d have to refactor everywhere the repository is used. How can I improve/fix this?

I’ve provided a little diagram of the flow:

data flow

Answer

I’m sure there’s probably a better solution but I simply introduced another layer of abstraction

enter image description here

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