Question about Joins

suneetshah2000 · **Joined:** Thu Jan 24, 2008 1:35 am **Posts:** 9

Hello:

In the tables below I have a Many to Many relationship between Group and Role. GroupRole does the linking between these tables.

In the objects below, is it necessary to use the intermediary object to facilitate the linking?

ie: In the Group object I have a collection of

Code:

* Does this have to GroupRoles or can I have a collection Roles and if so, how would I do that?

Ultimately, I would like to expose my pojo's as web services. However, because I have Role object in Group and Group object in Role, I am creating a circular reference. How do most people avoid this?

thanks for you help.

Group

Code:

   <class name="Group" table="GRP" >

        <comment></comment>
        <id name="grpId" type="string">
            <column name="GRP_ID" length="20" />
            <generator class="assigned" />
        </id>
        <property name="grpName" type="string">
            <column name="GRP_NAME" length="40">
                <comment></comment>
            </column>
        </property>
 
        <property name="companyId" type="string">
            <column name="COMPANY_ID" length="20">
                <comment></comment>
            </column>
        </property>
        <property name="parentGrpId" type="string">
            <column name="PARENT_GRP_ID" length="20">
                <comment></comment>
            </column>
        </property>

        <property name="groupClass" type="string">
            <column name="GROUP_CLASS" length="40">
                <comment></comment>
            </column>
  
        <set name="groupRoles" cascade="all-delete-orphan" lazy="true" inverse="true">
            <key>
                <column name="GRP_ID" length="20" not-null="true">
                    <comment></comment>
                </column>
            </key>
            <one-to-many class="GroupRole" />
        </set>
               
    </class>

Role

Code:

<hibernate-mapping>
    <class name="Role" table="ROLE" >
        <comment></comment>
        <id name="roleId" type="string">
            <column name="ROLE_ID" length="20" />
            <generator class="assigned" />
        </id>
        <property name="serviceId" type="string">
            <column name="SERVICE_ID" length="20">
                <comment></comment>
            </column>
        </property>
        <property name="roleName" type="string">
            <column name="ROLE_NAME" length="40">
                <comment></comment>
            </column>
        </property>

        <set name="grpRoles" fetch="select" cascade="all-delete-orphan">
            <key>
                <column name="ROLE_ID" length="20" not-null="true">
                    <comment></comment>
                </column>
            </key>
            <one-to-many class="GroupRole" />
        </set>
     
    </class>
</hibernate-mapping>

GroupRole

Code:

<hibernate-mapping>
    <class name="GroupRole" table="GRP_ROLE" >
        <comment></comment>
        <id name="grpRoleId" type="string">
            <column name="GRP_ROLE_ID" length="20" />
              <generator class="SequenceGenerator">
                 <param name="table">sequence_gen</param>
                 <param name="column">next_id</param>
                 <param name="attribute">GRP_ROLE_ID</param>
               </generator>
        </id>

        <many-to-one name="role" class="Role" fetch="select">
            <column name="ROLE_ID" length="20" not-null="true">
                <comment></comment>
            </column>
        </many-to-one>
        <many-to-one name="group" class="Group" fetch="select">
            <column name="GRP_ID" length="20" not-null="true">
                <comment></comment>
            </column>
        </many-to-one>


        <property name="serviceId" type="string">
            <column name="SERVICE_ID" length="20" not-null="true">
                <comment></comment>
            </column>
        </property>        

    </class>
</hibernate-mapping>

sanne.grinovero · **Posted:** Mon May 19, 2008 6:15 pm

Hi,

Quote:

I am creating a circular reference. How do most people avoid this?

you don't need to make the relationship bidirectional.

If you use serialized entities you don't need to be concerned with circularity.

Quote:

In the objects below, is it necessary to use the intermediary object to facilitate the linking?

Yes you need the intermediate object because of SERVICE_ID in your bridge table; if you didn't have properties on the link you could avoid the extra entity.

kind regards,