HI friends,

I have a design, you can find the ER diagram on http://213.42.180.226/problem.jpg. Basically there is a many-to-many relationship between Book and Explainer of a book, the result relation has a one-to-many relation with pages (please visit http://213.42.180.226/problem.jpg to understand it thoroughly). The problem is that it shows an Exception "Foreign Key XXX must have same number of columns as the referenced primary key".

Has anybody gone through such case ? Please advise.

Look forward to hearing from you

Yours,
Zaid

Hibernate version:3.0

Mapping documents:

<class name="Books" table="books">
<id name="bookId" column="book_id" type="integer">
<generator class="native"/>
</id>

<property name="bookName" column="book_name" type="string" not-null="true" />
<set name="explainers" table="explainers_books">
<key column="book_id"/>
<many-to-many class="Explainers" column="explainer_id"/>
</set>

</class>


<class name="Explainers" table="explainers">
<id name="explainerId" column="explainer_id" type="integer">
<generator class="native"/>
</id>

<property name="explainerName" column="explainer_name" type="string" not-null="true" />

<set name="books" table="explainers_books">
<key column="explainer_id"/>
<many-to-many class="Books" column="book_id"/>
</set>

</class>


<class name="ExplainersBooks" table="explainers_books">
<id name="explainerBookId" column="explainer_book_id" type="integer">
<generator class="native"/>
</id>

<property name="bookId" column="book_id" type="integer" not-null="true" />
<property name="explainerId" column="explainer_id" type="integer" not-null="true" />

<set name="pages">
<key column="page_id"/>
<one-to-many class="Pages"/>
</set>

</class>


<class name="Pages" table="pages">
<id name="pageId" column="page_id" type="integer">
<generator class="native"/>
</id>

<property name="explainerBookId" column="explainer_book_id" type="integer" not-null="true" />
<property name="pageName" column="page_name" type="string" not-null="true" />
</class>



Code between sessionFactory.openSession() and session.close():

Books book=(Books)sess.load(Books.class,new Integer(1));
System.out.println("book="+book.getExplainers().size());


Full stack trace of any exception that occurs:

%%%% Error Creating SessionFactory %%%%
org.hibernate.MappingException: Foreign key (FK657EFC4EA1D5846:pages [page_id])) must have same number of columns as the referenced primary key (explainers_books [explainer_id,book_id])
at org.hibernate.mapping.ForeignKey.alignColumns(ForeignKey.java:86)
at org.hibernate.mapping.ForeignKey.setReferencedTable(ForeignKey.java:51)
at org.hibernate.cfg.Configuration.secondPassCompileForeignKeys(Configuration.java:976)
at org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:921)
at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:999)
at com.zaid.model.hibernate.SessionFactory.currentSession(SessionFactory.java:49)
at com.zaid.struts.action.GetAddressesAction.execute(GetAddressesAction.java:49)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:419)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:224)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1194)
at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:856)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:744)
at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:527)
at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:80)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)
at java.lang.Thread.run(Thread.java:595)
[ WARN] 08:47:00 (RequestProcessor.java:processException:516)
Unhandled Exception thrown: class java.lang.NullPointerException

[ERROR] 08:47:00 (StandardWrapperValve.java:invoke:253)
Servlet.service() for servlet action threw exception



Name and version of the database you are using: MySQL 4.1

Zaid,

What you are trying to do is make the association bidirectional. The natural direction of this relationship is a many-to-one from Pages to ExplainerBooks.

You should first specify a many-to-one relationship in Pages for ExplainerBooks. After that set the inverse=true for the Pages set in ExplainerBooks. I think that should do it.

-Pratik

Hi Pratik,

Thanks for your reply. I tried to make it bidirectional, however it didn't work, same error message.

I even tried to remove the <one-to-many> in ExplainerBooks and added the <many-to-one> in Pages configuration, but it didn't work as well.

I think the problem is that Hibernate treats the combination of foreign keys in the middle Class (ExplainerBooks) as a primary key !.

Any suggestions ?

Thanks,
Zaid

Pratik, I found it

Simply, use idbag instead of set, because it is the only which can generate primary keys

in Explainers, replace the <SET> with the following:


<idbag name="books" table="explainers_books">
<collection-id type="integer" column="explainer_book_id">
<generator class="native"></generator>
</collection-id>
<key column="explainer_id"/>
<many-to-many class="Books" column="book_id"/>
</idbag>