Need help with many-to-many

Christian Gmeiner · **Joined:** Sun May 07, 2006 7:40 pm **Posts:** 3

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Hibernate version:
3.x

Mapping documents:

Equipment.hbm.xml

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">
<!-- Generated 05.05.2006 11:23:58 by Hibernate Tools 3.1.0.beta5 -->
<hibernate-mapping>
    <class name="database.EquipmentData" table="equipment" catalog="busmaster">
        <comment></comment>
        <id name="equipmentId" type="int">
            <column name="equipment_id" />
            <generator class="native" />
        </id>
        <property name="internalId" type="string">
            <column name="internal_id" length="20" not-null="true">
                <comment></comment>
            </column>
        </property>
        <property name="name" type="string">
            <column name="name" length="100" not-null="true">
                <comment></comment>
            </column>
        </property>
        <property name="requiredseats" type="short">
            <column name="requiredseats" not-null="true">
                <comment></comment>
            </column>
        </property>
        <property name="requiredstandings" type="short">
            <column name="requiredstandings" not-null="true">
                <comment></comment>
            </column>
        </property>
        <property name="deleted" type="boolean">
            <column name="deleted" not-null="true">
                <comment></comment>
            </column>
        </property>
    </class>
</hibernate-mapping>

Bus.hbm.xml:

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">
<!-- Generated 05.05.2006 11:23:58 by Hibernate Tools 3.1.0.beta5 -->
<hibernate-mapping>
    <class name="database.BusData" table="bus" catalog="busmaster">
        <comment></comment>
        <id name="busId" type="int">
            <column name="bus_id" />
            <generator class="native" />
        </id>
        <property name="internalId" type="string">
            <column name="internal_id" length="20" not-null="true">
                <comment></comment>
            </column>
        </property>
        <property name="seats" type="short">
            <column name="seats" not-null="true">
                <comment></comment>
            </column>
        </property>
        <property name="standingrooms" type="short">
            <column name="standingrooms" not-null="true">
                <comment></comment>
            </column>
        </property>
        <property name="licenceplate" type="string">
            <column name="licenceplate" length="20">
                <comment></comment>
            </column>
        </property>
        <property name="technical" type="string">
            <column name="technical" length="65535">
                <comment></comment>
            </column>
        </property>
        <many-to-one name="category" class="database.BuscategoryData" not-null="true"/>
        <!--
        <property name="buscategoryId" type="int">
            <column name="buscategory_id" not-null="true">
                <comment></comment>
            </column>
        </property>
        -->
        <property name="internalbus" type="boolean">
            <column name="internalbus" not-null="true">
                <comment></comment>
            </column>
        </property>
        <property name="deleted" type="boolean">
            <column name="deleted" not-null="true">
                <comment></comment>
            </column>
        </property>
        <!-- here we map our list -->
        <list name="equipment" table="useableequipment">
...........................
           <many-to-many class="database.EquipmentData"/>
        </list>
    </class>
</hibernate-mapping>

DB: http://x-factor.dyndns.org/~austriancod ... 0agent.png

As you can see, i want to have a List in Busclass, so that i can do this:

Code:

Bus b = new Bus();
Equipment e = new Equipment();
e.set...

Equipment e1 = new Equipment();
e1.set...

List useabelequipment = new List();
useabelequipment.add(e);
useabelequipment.add(1);

b.setequipment(useabelequipment);

Can sombody help me to finish my mapping? I need to store the bus_id and the equipment_id in the table useabelequipment

Thanks for any help,
Christian[/code]

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

I think that you probably want a set or bag, not a list. A list has a list index, so unless you're planning on having a list index column in your mapping table, you can't use a list. (A list index column would be something to the effect of a column with an ordinal in it.. a "position index")

The mapping for a many-to-many collection is usually done like this:

Code:

<set name="Equipemnt" table="BusEquipmentLinkTable">
  <key column="ColumnInBusTableThatLinksToLinkTable" not-null="true"/>
  <many-to-many class="Equipment" column="ColumnInLinkTableThatLinksToEquipmentTable"/>
</set>

If the link from the Equipment table to the link table isn't via Equipment's id column, then you can put a property-ref="NameOfPropertyInEquipmentWhoseColumnMapsToLinkTable" in the many-to-many element.

The field/property in the java class can be either Collection or Set type. If you're committed to using List type, you can replace <set> with <bag>, but there are some performance penalties if you do that.