Hibernate Community • View topic - mapping java Collections map with a List as value type

View unanswered posts | View active topics

Board index » Hibernate & Java Persistence » Hibernate Users

All times are UTC - 5 hours [ DST ]

mapping java Collections map with a List as value type

Page 1 of 1

[ 4 posts ]

Previous topic | Next topic

Author

Message

vhockey86

Post subject: mapping java Collections map with a List as value type

Posted: Fri Jan 27, 2006 7:05 pm

Newbie

Joined: Fri Jan 27, 2006 6:55 pm
Posts: 2

Hibernate version:
3
Mapping documents:

Code:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
   "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
   "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>

   <class name="src.Person" table="PERSONS">
       <id name="id" type="long" column="uid">
           <generator class="increment"/>
       </id>
       
       <property name="name" column="names" type="string"/>
       
       <joined-subclass name="src.Student" table="STUDENTS">
           <key column="uid"/>
           <property name="grade" column="grade" type="integer"/>
           <property name="sessionCount" column="sessions" type="integer"/>
           <property name="level" column="boardLevel" type="integer"/>
           <property name="position" column="boardPosistion" type="integer"/>
           <map name="scores">
              <key column="id"/>
              <index column="gradeID" type="integer"/>
              <element column="score" type="double"/>
           </map>        
       </joined-subclass>
         
       <joined-subclass name="src.Teacher" table="TEACHERS">
          <key column="uid"/>
          <property name="password" column="password" type="string"/>
       </joined-subclass>
       
       <joined-subclass name="src.BoardMember" table="BOARDMEMBERS">
          <key column="uid"/>
          <property name="password" column="password" type="string"/>
       </joined-subclass>
   </class>
   
</hibernate-mapping>

Hello. I have an inheritence model that has a "Person" as the Parent class and "Student"/"Teacher"/"BoardMember" as the sub-classes.

The student class contains an instance variable called "scores", which is a Map<Integer,List<Double>>. I cant seem to figure out how to setup the mapping file to accomodate the list of doubles as an element of the map.

Ive been reading about many-to-many and one-to-many associations but cant seem to wrap my head around how it would be useful in this situation.

If anyone could tell me how this mapping would be possible I'd appreciate it.

Thanks,
Andrew

Top

skalinic

Post subject: Mapping a MultiMap

Posted: Fri Jan 27, 2006 8:07 pm

Beginner

Joined: Mon Mar 14, 2005 6:07 pm
Posts: 36

A Map<Integer,List<Double>> is not a simple Map - it's a MultiMap. I'm nearly certain that Hibernate does not support MultiMaps directly.

One way to deal with this problem is to use composite map keys (see section 8.3 of the documentation). You'll need to build a new key class to use instead of Integer. That class will contain two integers - one is the original key, the other is the sequence number of the grade in the list of grades. So instead of this Map

100->{3.5, 3.6, 4.0 }
101->{2.7, 3.0, 2.9 }

you'll build this:

(100,0) -> 3.5
(100,1) -> 3.6
(100,2) -> 4.0
(101,0) -> 2.7
(101,1) -> 3.0
(101,2) -> 2.9

You can put the same Java interface on top of this new Map, and make the new composite key package-private to hide the details completely. You'll have to write a bit more code too, but I'm certain that all programmers enjoy writing code, so the more - the better :-)

Good luck!

Top

vhockey86

Post subject:

Posted: Fri Jan 27, 2006 8:51 pm

Newbie

Joined: Fri Jan 27, 2006 6:55 pm
Posts: 2

So there's no way that I could have the element of the map be.... say an integer? And then use that integer collumn as the key of a table join, where that table contains the double values?

I also don't completely follow your solution... but maybe it'll make more sense when I get some time to read the 8.3 documentation.

Alternatively does anyone know of another solution for storing the same data?

Essentially all I need is a list of doubles corresponding to 5 different gameIDs. I suppose I could just store 5 lists in the student class or a List of Lists?

Top

priyankaMahajan

Post subject: Re: mapping java Collections map with a List as value type

Posted: Tue Nov 10, 2009 4:05 am

Newbie

Joined: Mon Oct 12, 2009 6:07 am
Posts: 7

Even I have the same issue..any help wi=ould be appreciated

Top

Page 1 of 1

[ 4 posts ]

Board index » Hibernate & Java Persistence » Hibernate Users

All times are UTC - 5 hours [ DST ]

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum