如何得到/放Kotlin内地图或地图的地图

任何人都知道我怎样才能“把/放”在kotlin内的地图？

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

我怎样才能把以下的书籍细节放在上面的地图上？

 var books: MutableList = this.bookDao.findAll() 

预计存储将像>

 var bookDetailsMap: MutableMap<book.publisherId, MutableMap> 

Answer 1

成功做到这一点：

举例：

 var bookDetailsMap : Map> = 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]!! }