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Bi-Directional many-to-many with composite keys

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nicks

Post subject: Bi-Directional many-to-many with composite keys

Posted: Mon Jan 21, 2008 6:11 pm

Newbie

Joined: Wed Jan 09, 2008 11:30 pm
Posts: 9

I just cant seem to come up with a valid mapping.

Code:

<hibernate-mapping>
   <class name="mypackage.Tokens" table="TOKENS"
      schema="PUBLIC">
      <composite-id name="id"
         class="mypackage.TokensId">
         <key-property name="appid" type="string">
            <column name="APPID" length="34" />
         </key-property>
         <key-property name="token" type="string">
            <column name="TOKEN" length="128" />
         </key-property>
      </composite-id>
      <set name="belongsTo" table="TokenGroups">
         <key column="Tokens"/>
         <many-to-many column="GroupsId" class="mypackage.Groups"/>
      </set>
   </class>
</hibernate-mapping>

Code:

<hibernate-mapping>
   <class name="mypackage.Groups" table="GROUPS"
      schema="PUBLIC">
      <composite-id name="id"
         class="mypackage.GroupsId">
         <key-property name="appid" type="string">
            <column name="APPID" length="34" />
         </key-property>
         <key-property name="groupname" type="string">
            <column name="GROUPNAME" length="128" />
         </key-property>
      </composite-id>
      <set name="members" inverse="true" table="UserGroups">
         <key column="GroupID"/>
         <many-to-many column="UserID" class="mypackage.Users"/>
      </set>
      <set name="tokenSet" inverse="true" table="TokenGroups">
         <key column="Group"/>
         <many-to-many column="Token" class="mypackage.Tokens"/>
      </set>
   </class>
</hibernate-mapping>

this seems to be close, but I get a complaint about not having enough columns in the foreign key relationship

Code:

org.hibernate.MappingException: Foreign key (FKF5E4090D1085596A:TokenGroups [Token])) must have same number of columns as the referenced primary key (TOKENS [APPID,TOKEN])

I've been reading through the documentation, and googling, but I have yet to find something that points me n the right direction

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nicks

Post subject:

Posted: Mon Jan 21, 2008 6:13 pm

Newbie

Joined: Wed Jan 09, 2008 11:30 pm
Posts: 9

I'd better actually ask the question;

Can somebody please tell me what I'm doing wrong, or which step I've missed?

Thank you.

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Clay

Post subject:

Posted: Tue Jan 29, 2008 1:02 pm

Beginner

Joined: Mon Mar 07, 2005 6:23 pm
Posts: 21

Did you auto-generate your mapping files from Hibernate Tools? If I remember correctly, it has a problem accurately doing many-to-many mappings that use composite keys...

Regardless, you need to reference both pk/fk columns in your many-to-many setup - notice it's only referencing one of them on both sides.

something like this might work:

Code:

    
<set name="belongsTo" table="TokenGroups">
      <key>
        <column name="APPID"/>
        <column name="TOKEN"/>
      </key>
      <many-to-many class="mypackage.Groups">
        <column name="APPID"/>
        <column name="GROUPNAME"/>
      </many-to-many>
</set>

Are you sure you've got your keys set up right? both Groups and Tokens both have an "APPID" column, but your many-to-many mapping in Groups references a GroupID column...

Anyway, the basic idea is that your many-to-many table should include the PK(s) from the tables on both sides.

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