Sugestion: Give an option for returning a Map instead a List

RubemAzenha · **Posted:** Wed Feb 22, 2006 12:07 pm

Hello there,
I'm currently using Hibernate in a project here.
In a given moment, i have to use a query for searching. The Query returns a List. But I have to get this List and put it into a map strucure...

Like this:

Code:

List peoples = dao.findByAge(age);  //DAO using Hibernate
Map peoplesMap = new HashMap();
for (Iterator it =  peoples.iterator(); it.hasNext; ) {
    People people = (People) it.next();
    peoplesMap.put(people.getName(), people);
}

So the list will be "iterated" twice: once when Hibernate creates it with the results of the query and when my code gets this list and puts its data do a Map.
This may overhead the system. Using pure JDBC, i would create the map while iterating the ResultSet.

Maybe Hibernate next version should have e feature that permits return a map rather than a List, letting me choice which property will be the key and putting the intire object as the value.

Or maybe hibernate do this but I didn't found in the docs :)

the-gtm · **Joined:** Wed Feb 08, 2006 3:59 pm **Posts:** 75

Query.iterate() is your friend :-) You get an Iterator without the (light) overhead of building/fetching a list.

RubemAzenha · **Posted:** Wed Feb 22, 2006 9:36 pm

No, I still have to iterate the List.

the-gtm · **Joined:** Wed Feb 08, 2006 3:59 pm **Posts:** 75

I didn't say Query.list().iterator(), I said Query.iterate(). You get an iterator which isn't backed by a List.

alexism · **Joined:** Thu Feb 16, 2006 9:53 am **Posts:** 24

I'm facing the same problem but it seems that the "iterate() solution" is not really perfect :

http://www.hibernate.org/hib_docs/v3/re ... ng-iterate

Quote:

This will only usually be the case if you expect that the actual entity instances returned by the query will already be in the session or second-level cache.
If they are not already cached, iterate() will be slower than list() and might require many database hits for a simple query, usually 1 for the initial select which only returns identifiers, and n additional selects to initialize the actual instances.

the-gtm · **Joined:** Wed Feb 08, 2006 3:59 pm **Posts:** 75

Thanks for this info, I didn't realize iterate() worked that way. Anyway, I don't think building a list and then fectching it is a big performance it, execpt of course if it has thousands of records.

By the way : putting People objects in a map with 'name' as a key doesn't sound like a good idea to me. Are you sure two people can't have the same name ?

RubemAzenha · **Posted:** Fri Feb 24, 2006 11:28 am

That's only an example... I cannot paste a real source of my application :(
The key putted in the map is a non-pk, but unique collumn.