RxJava. Correct way to generate ViewObject by few sources

Question

I have two entity classes, which stores in SQLite : UserEntity and SessionInfoEntity :

public class UserEntity{
    private Long id;
    private String userName;
    // ....
}

public class SessionInfoEntity{
    private Long id;

    private Date beginSessionDate;
    private Date endSessionDate;
    // ....
}

User can have many sessions (one-to-many relation).

I have a repository, which provides necessary methods to get data (RxJava observables) from my SQLite database:

public class MyRepository{
    public Observable<List<UserEntity>> getAllUsers(){/* ... */}
    public Observable<SessionInfoEntity> getLastSessionInfoForUser(Long userId){/* ... */} // returns info of last session for user with id=userId
}

I need to generate next ViewObject for each User, using MyRepository 's methods and RxJava :

public class UserViewObject {
    private String userName;
    private Integer lastSessionDurationInHours;
    // ....
}

In turns out that I need to call getLastSessionInfoForUser() for each User in order to create UserViewObject .

QUESTION: How I can generate UserViewObject using RxJava correctly?

I'm trying to start doing this this way:

myRepository
            .getAllUsers()
            .flatMap(lst -> Observable.from(lst))
            .flatMap(ve -> getLastSessionInfoForUser(ve.getId())
            .map(lse -> /* ?????  */) // In this operator I lose access to current user => I can't generate UserViewObject, because I haven't access to ve.getUserName() method

PS: I can't write method in MyRepository, which will be returns object with whole information.

PPS: In the future, new methods will be added that are related to the User entity (like getLastSessionInfoForUser() method).

Answer 1

You can add the map in the last flatMap . Like that you have access to ve .

myRepository
        .getAllUsers()
        .flatMap(lst -> Observable.from(lst))
        .flatMap(ve -> getLastSessionInfoForUser(ve.getId()).map(lse -> /* ... */))