Kotlin中如何实现Network Service模型与Room Entities双向转换

前置修正 #

你当前的DatabaseRoot里的@Embedded注解使用有误，@Embedded仅支持嵌套普通数据类，无法作用于列表类型。你已经实现了对应列表的TypeConverter，直接删除@Embedded注解即可，Room会自动调用转换器将List<DatabaseResults>序列化为JSON字符串存入数据库。
另外记得在你的Room Database类上添加转换器注册注解，确保转换器生效：

@Database(entities = [DatabaseRoot::class], version = 1)
@TypeConverters(DatabaseResultsTypeConverter::class) // 新增这行
abstract class AppDatabase : RoomDatabase() {
    // ... DAO定义
}

双向转换代码实现 #

嵌套列表的转换逻辑很简单，在外层对象转换时，对内层列表的每一项单独做类型映射即可，具体实现如下：

网络模型转Room实体 #

fun List<Root>.asDatabaseModel(): Array<DatabaseRoot> {
    return map { networkRoot ->
        DatabaseRoot(
            page = networkRoot.page,
            // 对results列表每一项做类型转换
            results = networkRoot.results.map { networkResult ->
                DatabaseResults(
                    adult = networkResult.adult,
                    backdrop_path = networkResult.backdrop_path,
                    genre_ids = networkResult.genre_ids,
                    id = networkResult.id,
                    original_language = networkResult.original_language,
                    original_title = networkResult.original_title,
                    overview = networkResult.overview,
                    popularity = networkResult.popularity,
                    poster_path = networkResult.poster_path,
                    release_date = networkResult.release_date,
                    title = networkResult.title,
                    video = networkResult.video,
                    vote_average = networkResult.vote_average,
                    vote_count = networkResult.vote_count
                )
            },
            total_pages = networkRoot.total_pages,
            total_results = networkRoot.total_results
        )
    }.toTypedArray()
}

Room实体转网络域模型 #

fun List<DatabaseRoot>.asDomainModel(): List<Root> {
    return map { dbRoot ->
        Root(
            page = dbRoot.page,
            // 反向转换列表每一项
            results = dbRoot.results.map { dbResult ->
                Results(
                    adult = dbResult.adult,
                    backdrop_path = dbResult.backdrop_path,
                    genre_ids = dbResult.genre_ids,
                    id = dbResult.id,
                    original_language = dbResult.original_language,
                    original_title = dbResult.original_title,
                    overview = dbResult.overview,
                    popularity = dbResult.popularity,
                    poster_path = dbResult.poster_path,
                    release_date = dbResult.release_date,
                    title = dbResult.title,
                    video = dbResult.video,
                    vote_average = dbResult.vote_average,
                    vote_count = dbResult.vote_count
                )
            },
            total_pages = dbRoot.total_pages,
            total_results = dbRoot.total_results
        )
    }
}

可选优化 #

如果不想手动逐个映射字段，可以引入MapStruct框架自动生成转换代码，减少模板代码量，同时避免手写字段映射出错的问题。

内容的提问来源于stack exchange，提问作者Víctor Martín