Clash Royale CLAN TAG#URR8PPP

Android Combine 2 Lists of data one from Room LiveData and 1 from Observable

I am building an app that for now have one main data model Character, I'm using Room as local DB and retrofit2 for API calls.
The user can set a Character as favorite and when this happens this character is stored in local DB (only local DB know about favorite characters of a current user, this app does not store any data on remote servers just use API to get a list of characters).
The question is when user load next time the app how to load the list from web and from local DB (Room return LiveData<List<Character>) and filter out from web list Characters which stored in local DB with the help of RxJava2 (I can use Observable as return from retrofit2) so when I show the list in RecyclerView there will be no duplicates.

Character

LiveData<List<Character>

Characters

For better understand of what i mean:
I have MainActivity which have MainViewModel, in MainViewModel i have CharacterRepository reference which know how to load data from web as (Call<CaharacterResponse> / Observable<CharacterResponse>) and load method from local DB Livedata<List<Character>> (this is list of Characters which marked as favorite by user).
what i want is when user load the application both the web and the local data will be loaded and then results will be filtered to remove duplicates.
*CharacterResponse have extra fields about web call result and one of the fields is List.

MainActivity

MainViewModel

MainViewModel

CharacterRepository

Call<CaharacterResponse> / Observable<CharacterResponse>

Livedata<List<Character>>

@Dao
public interface CharacterDao

@Query("SELECT * FROM character ORDER BY name")
LiveData<List<Character>> getAllFavoriteCharacters();

....


public interface ExampleClient

String BASE_URL = "http://gateway.example.com/public/";

@GET("characters/id")
Call<CharacterResponse> getCharacter(@Path("id")int id);


@GET("characters")
Call<CharacterResponse> getCharacters(@Query("limit") @Nullable Integer limit);

Observable<CharacterResponse> getCharacters();



1 Answer
1

In order to handle both LiveData and Observable in one way you can adapt them into each other by LiveDataReactiveStreams and Observable.fromPublisher().

LiveData

Observable

Observable.fromPublisher()

Then you'll have 2 Observables which provides data - one from web and other from local DB.

Observables

Observable.concatArrayEager

Or you can merge local with remote

local.mergeWith(remote)
.collect(() -> new HashSet<Integer>(), (set, v) -> set.add(v))
.flatMap(Observable::from)
.subscribe(System.out::println);

local.mergeWith(remote)
.collect(() -> new HashSet<Integer>(), (set, v) -> set.add(v))
.flatMap(Observable::from)
.subscribe(System.out::println);

Or you could use distinct operator to remove duplicates from Observable

Observable

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