Handling lists with RxJava and Retrofit in android

Question

I have couple of api calls to make (sequentially, asynchronously) and some of them returns lists. My api interface is given below.

@GET("/users/settings")
Observable<UserWrapper> getUserSettings();

@GET("/{username}/collections")
Observable<List<Item>> getItems(@Path("username") String userName);

@GET("/item/{id}")
Observable<ItemInfo> getItemInfo(@Path("id") int id);

@GET("/{username}/friends")
Observable<List<Friend>> getFriends(@Path("username") String userName);

Here's what I want to do sequentially:

• Get UserWrapper by calling getUserSettings()
• Save the user by calling saveUser(userWrapper)
• Get user's items by calling getItems(userWrapper.getUserName())
• Get each item's information by calling getItemInfo(item.getId())
• Save each itemInfo by calling saveItem(itemInfo)
• Get user's friends by calling getFriends(userWrapper.getUserName())
• Save each friend by calling saveFriend(friend)

Now I am new to RxJava and do not know how to handle lists. I watched one of Jake Wharton's slides and found that he uses a function flattenList() but I don't know its definition. It would be great if you can help composing this chain.

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Update 1

This is as far I've gotten now:

mApiService.getUserSettings()
            .map(this::saveUser)
            .flatMap(userWrapper -> mApiService.getItems(userWrapper.getUserName()));
            .flatMapIterable( ? "How to iterate for each item" ? );

---

Update 2

I am trying to write something like this

mApiService.getUserSettings()
    .map(this::saveUser)
    .flatMap(userWrapper -> mApiService.getItems(userWrapper.getUserName()))
    .someMethodToIterateThroughEachItem(item -> mApiService.getItemInfo(item))
    .map(this::saveItem)
    .someMethodThatCanCallUserWrapperAgain(userWrapper -> mApiService.getFriends(userWrapper.getUserName()))
    .someMethodToIterateThoughEachFriend(friend -> saveFriend(friend))

Answer 1

RxJava has added flatMapIterable. So you don't need flattenList now. E.g.,

  Observable<UserWrapper> o =
       getUserSettings()
       .doOnNext(this::saveUser)
       .flatMap(user -> getItems(user.getUserName())
                        .flatMapIterable(items -> items)
                        .flatMap(item -> getItemInfo(item.getId()))
                        .doOnNext(this::saveItem)
                        .toList()
                        .map(ignored -> user))
        .flatMap(user -> getFriends(user.getUserName())
                         .flatMapIterable(friends -> friends)
                         .doOnNext(this::saveFriend)
                         .toList()
                         .map(ignored -> user)
        );
    o.subscribe(...);