Collection inside Collection

pyradonis · **Joined:** Sun Apr 30, 2006 9:52 am **Posts:** 2

Hi all!

Does anyone know a way of Mapping a Collection that holds a Collection as its value:

My problem:

I need something like that Map<Objec,Set<Object>>

is this possible, and if, how?

thx

michael

// edit: noob question or just no answer?

tenwit · **Joined:** Thu Dec 23, 2004 9:08 pm **Posts:** 2008

No, as far as I'm aware, you'd have to make an intermediate class, though if you have the DB shape to model Map<Object, Set<Object>>, then the mapping pretty much writes itself. You'd just end up with Class1 containing a Map<Object, Class2>, and Class2 only has two members: its id (being the map-key from Class1) and the Set<Object> that you really wanted to map.

pyradonis · **Joined:** Sun Apr 30, 2006 9:52 am **Posts:** 2

thx for your answer!

Thats exactly how i solved that problem so far. i only wanted to know if there is a better solution. it doesnt seems so, but i can live with that.
thx for your( the only ) answer.

greets

pyradonis

tenwit · **Joined:** Thu Dec 23, 2004 9:08 pm **Posts:** 2008

On the plus side, this way of mapping means that the set is cached separately from the map, as they're in separate objects. So if one changes, the other one isn't invalidated in the cache. This solution has performance benefits.

Cloud. Silver lining. Voila!