Hi im trying to build a `Map<MyDo, List<MyDO>>` from my local database table which has t...

# android

[Tower Guidev2]

Hi
im trying to build a Map<MyDo, List<MyDO>> from my local database table which has the following columns

[Tower Guidev2]

the tables rows consist of both the parent categories (with parent_category = NULL) and the child categories
i wish to build a map that has a key set of parent categories with an associated map value of a list of all the parents child categories

my sql query simply returns a list of all rows contained in the db table and i want to construct the map using kotlin available list functions
such as sortedBy, groupBy etc...

all my attempts so far have failed. and all i can manage is to build a map with a single unique entry in the list of children
is it possible to construct the desired map using kotlin functions alone?

[Tower Guidev2]

@kenkyee might be worth letting me ask my question before flagging as not kotlin

[Eugen Martynov]

I hope MyDo are the data classes or classes that have proper equals implemented. You can do it with SQL. But with Kotlin it will be something like

val rows = <get list of rows from table>
val map = rows.map{ mydo -> 
   mydo to rows
            .filter{ it.parent_category == mydo.category_id }
}
.filter{ pair -> pair.second.isNotEmpty() }
.toMap()