使用Single<Boolean>过滤

Question

我想过滤一个流()，过滤器必须提供一个谓词我如何使用RxJava实现这一点，我正在使用房间持久性数据库，如果数据库还没有包含新字段，我想添加它们，我的问题是使用doesDatabaseContainSong()方法。

我是RX Java的新手，代码是Kotlin和Java的混合

    // 1. ADD NEW SONGS TO DATABASE
songs.stream()
        .filter(song -> !doesDatabaseContainSong(song, mViewModel))
        .forEach(this::addSongToDatabase);

我希望下面的函数(DoesDatabaseContainSong)返回一个布尔值，而不是返回Single< Int >

public static boolean doesDatabaseContainSong(Song song, SongViewModel model) {
    int result = model.doesDatabaseContainSong(song.getId(), Type.GOOGLE_DRIVE.name());
    return result != 0;
}

视图模型

fun doesDatabaseContainSong(mId: String): Single<Int> {
    return repository.doesDatabaseContainSong(mId)
}

存储库

fun doesDatabaseContainSong(mId: String): Single<Int> {
    return songDao.doesDatabaseContainSong(mId)
}

“道”

@Query("SELECT COUNT(id) from song_table WHERE id = :mId")
fun doesDatabaseContainSong(mId: String): Single<Int>

Answer 1

DAO (已将返回类型更改为布尔值)

@Query("SELECT COUNT(id) from song_table WHERE id = :mId")
fun doesDatabaseContainSong(mId: String): Single<Boolean>

存储库(将返回类型更改为布尔值)

fun doesDatabaseContainSong(mId: String): Single<Boolean> {
    return songDao.doesDatabaseContainSong(mId)
}

视图模型(已将返回类型更改为布尔值)

fun doesDatabaseContainSong(mId: String): Single<Boolean> {
    return repository.doesDatabaseContainSong(mId)
}

(已将返回类型更改为布尔值)

public static Single<Boolean> doesDatabaseContainSong(Song song, SongViewModel model) {
    return model.doesDatabaseContainSong(song.getId(), Type.GOOGLE_DRIVE.name());
}

现在是最终的代码：

songs
    .stream()
    .flatMap(doesContainSong -> doesDatabaseContainSong(song, mViewModel))
    .filter(doesContainSong -> !doesContainSong)
    .forEach(this::addSongToDatabase);

希望这能有所帮助。