java RxJava通过匹配属性值连接可观察流

Question

假设我有两条可观测的流

Observable<Book> books;
Observable<Movie> movies;

当它们有一个匹配的属性时，我如何连接它们？类似于下面的psudo代码：

Observable<BookMoviePair> pairs = books.join(movies)
    .where((book, movie) -> book.getId() == movie.getId()))
    .return((book, movie) -> new BookMoviePair(book, movie));

Answer 1

一种方法是：

Observable<BookMoviePair> pairs =
        books.flatMap(book -> movies
                .first(movie -> movie.getId() == book.getId())
                .map(movie -> new BookMoviePair(book, movie)));