如何获取/放置Kotlin内部地图或地图地图

Question

任何人都知道如何在kotlin中“获取/放置”内部地图？

var bookDetailsMap: MutableMap<Long, MutableMap<Long, Book>> = mutableMapOf()

如何将书籍细节下方“放入”上面的地图

var books: MutableList<Book> = this.bookDao.findAll()

预计存储将类似于＆gt;

var bookDetailsMap: MutableMap<book.publisherId, MutableMap<book.bookId, Book>>

Answer 1

成功实现这一目标：

举例：

var bookDetailsMap : Map<Long, Map<Long, BookDetail>> = hashMapOf()

this.bookDetailsMap = this.bookDao.findAll().groupBy { 
   it.publisherId
}.mapValues { 
   it.value.associateBy { it.bookId} 
}

获取示例：

var bookDetail : BookDetail = BookDetail ()

if (this.bookDetailsMap .containsKey(this.publisherId)) {
    bookDetail = this.bookDetailsMap [this.publisherId]!![this.bookId]!!
}