Mapping: Have a Set return a List

Laurens · **Joined:** Wed Apr 05, 2006 3:19 pm **Posts:** 43

Hibernate version:
version 3.1.3, March 20, 2006

Mapping documents:
The one for Unittype

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="objects.Unittype" table="unittypes">
      <id name="typeID" column="typeID">
            <generator class="native" />
        </id>
        <property name="typeName" />

      <set name="units" inverse="true" cascade="all-delete-orphan">
          <key column="unittypeID" />
          <one-to-many class="objects.Unit" />
      </set>
    </class>
</hibernate-mapping>

The one for Unit

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="objects.Unit" table="units">
      <id name="unitID" column="unitID">
            <generator class="native" />
        </id>
        <property name="unitName" />
        <property name="typeID" />

      <many-to-one name="unittype" class="objects.Unittype" column="unittypeID" not-null="true" />
    </class>
</hibernate-mapping>

How do I return a "List" of units instead of a "Set"? I tried to change set to list, but that gave an error...

Code:

<set name="units" inverse="true" cascade="all-delete-orphan">
   <key column="unittypeID" />
   <one-to-many class="objects.Unit" />
</set>

to

<list name="units" inverse="true" cascade="all-delete-orphan">
   <key column="unittypeID" />
   <one-to-many class="objects.Unit" />
</list>

kochcp · **Posted:** Thu Apr 06, 2006 3:51 pm

list requires an index be set

Laurens · **Joined:** Wed Apr 05, 2006 3:19 pm **Posts:** 43

Thanks a lot. I did a google search for "hibernate list id index" and found an example. First I tried searching for "hibernate set list" but that was just too generic to find a good result. I couldn't even find it in the documentation. (maybe I didn't look well enough?)

Anyway, right now it works. :) Maybe I'll be back for some more questions. I'm trying this for the first time and I must say: I like it!

Laurens · **Joined:** Wed Apr 05, 2006 3:19 pm **Posts:** 43

I had to add "update=false insert=false" to my "Unit" mapping because there was a duplicate field. I changed my mapping to scenario (1) and scenario (2). They both work.

Quote:

<?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="objects.Unit" table="units">
<id name="unitID" column="unitID">
<generator class="native" />
</id>
<property name="unitName" />
<property name="typeID" update="false" insert="false" (1) />

<many-to-one name="unittype" class="objects.Unittype" column="typeID" not-null="true" update="false" insert="false" (2) />
</class>
</hibernate-mapping>

The many-to-one mapping is because Unit has a parent -> Unittype. I wonder where the "update=fal....." should go: place (1) or place (2) (because they both work).

I also wonder if the property "typeID" is still needed, because it is already included in its parent: the object Unittype. If that's the case, should I still need to include the "update=....." piece?

kochcp · **Posted:** Fri Apr 07, 2006 9:24 am

place 2

Laurens · **Joined:** Wed Apr 05, 2006 3:19 pm **Posts:** 43

I'm getting a nullpointer if I try to do this:

Code:

Unittype ut = .......findbyid(some-correct-id);
@SuppressWarnings("unchecked")
List<Unit> list = ut.getUnits();

for(Unit unit : list){
   do something with unit (e.g. unit.getName() ) <-- NullpointerException
}

I know that the units don't get initialized in "ut.getUnits()", but my question is: how do you say to hibernate: "initialize these objects now!"?

Laurens · **Joined:** Wed Apr 05, 2006 3:19 pm **Posts:** 43

Quote:

I know that the units don't get initialized in "ut.getUnits()", but my question is: how do you say to hibernate: "initialize these objects now!"?

I want to correct myself: they DO get initialized when I do this:

Code:

List<..... list = (Lis....)ut.getList()

for(Unit unit : list){
  list.get(1).getName(); <-- does not throw any Exception
  unit.getName(); <-- Throws NullPointerException
}

Is it possible for a developer to look into this?
Thanks

Laurens · **Joined:** Wed Apr 05, 2006 3:19 pm **Posts:** 43

I tried a little debugging... I did the following:

Code:

int i = 0;
for(Unit unit : list){
   System.err.println("Listnr: "+ i++);
   if(unit != null) {
      System.err.println("Unitnr: "+ unit.getUnitID() +" - Unitname: "+ unit.getUnitName());   
   }
}

That gave me the following result:

Code:

Listnr: 0
Listnr: 1
Unitnr: 1 - Unitname: Unit 1
Listnr: 2
Listnr: 3
Listnr: 4
Listnr: 5
Listnr: 6
Listnr: 7
Unitnr: 7 - Unitname: Unit 2
Listnr: 8
Listnr: 9
Listnr: 10
Unitnr: 10 - Unitname: Unit 3
Listnr: 11
Unitnr: 11 - Unitname: Unit 4
Listnr: 12
Unitnr: 12 - Unitname: Unit 5

So basically, it means that the list gets filled with null values like this:

Code:

list(null,unit1,null,null,....)

because the database says: 1-unit1, 7-unit2, ... but I don't want that. I only want the units to be in the list, not null values. So like this:

Code:

list(unit1,unit2,...,unit12)

How do I do that?